diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2bd428906..702e9c73f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -18,10 +18,10 @@ jobs:
     steps:
     - uses: actions/checkout@v1
 
-    - name: Set up Ruby 2.6
+    - name: Set up Ruby 2.7
       uses: actions/setup-ruby@v1
       with:
-        ruby-version: 2.6.x
+        ruby-version: 2.7.x
 
     - name: Rubocop
       run: |
@@ -53,7 +53,7 @@ jobs:
     - name: Set up RVM
       run: |
         curl -sSL https://get.rvm.io | bash
-        
+
     - name: Set up Ruby
       run: |
         source $HOME/.rvm/scripts/rvm
diff --git a/Gemfile b/Gemfile
index 8ac63ce90..45aee7dbf 100644
--- a/Gemfile
+++ b/Gemfile
@@ -12,7 +12,7 @@ group :development, :test do
 end
 
 group :lint, :development do
-  gem 'rubocop', '~> 0.84.0'
+  gem 'rubocop', '~> 0.90.0'
   gem 'rubocop-performance', '~> 1.0'
 end
 
diff --git a/lib/faraday/adapter/em_http.rb b/lib/faraday/adapter/em_http.rb
index 156da5a52..f2d98c585 100644
--- a/lib/faraday/adapter/em_http.rb
+++ b/lib/faraday/adapter/em_http.rb
@@ -231,7 +231,7 @@ def running?
 
         def add(&block)
           if running?
-            perform_request { yield }
+            perform_request(&block)
           else
             @registered_procs << block
           end
diff --git a/lib/faraday/connection.rb b/lib/faraday/connection.rb
index e2ef528f0..3776253ee 100644
--- a/lib/faraday/connection.rb
+++ b/lib/faraday/connection.rb
@@ -429,7 +429,7 @@ def url_prefix=(url, encoder = nil)
     # @return [String] the new path prefix
     def path_prefix=(value)
       url_prefix.path = if value
-                          value = '/' + value unless value[0, 1] == '/'
+                          value = "/#{value}" unless value[0, 1] == '/'
                           value
                         end
     end
@@ -520,7 +520,7 @@ def build_exclusive_url(url = nil, params = nil, params_encoder = nil)
       base = url_prefix
       if url && base.path && base.path !~ %r{/$}
         base = base.dup
-        base.path = base.path + '/' # ensure trailing slash
+        base.path = "#{base.path}/" # ensure trailing slash
       end
       uri = url ? base + url : base
       if params
@@ -593,7 +593,7 @@ def find_default_proxy
       uri = ENV['http_proxy']
       return unless uri && !uri.empty?
 
-      uri = 'http://' + uri unless uri.match?(/^http/i)
+      uri = "http://#{uri}" unless uri.match?(/^http/i)
       uri
     end
 
diff --git a/lib/faraday/options.rb b/lib/faraday/options.rb
index b5af43d1b..ee198d8df 100644
--- a/lib/faraday/options.rb
+++ b/lib/faraday/options.rb
@@ -103,12 +103,10 @@ def empty?
     end
 
     # Public
-    def each_key
+    def each_key(&block)
       return to_enum(:each_key) unless block_given?
 
-      keys.each do |key|
-        yield(key)
-      end
+      keys.each(&block)
     end
 
     # Public
@@ -119,12 +117,10 @@ def key?(key)
     alias has_key? key?
 
     # Public
-    def each_value
+    def each_value(&block)
       return to_enum(:each_value) unless block_given?
 
-      values.each do |value|
-        yield(value)
-      end
+      values.each(&block)
     end
 
     # Public
diff --git a/lib/faraday/rack_builder.rb b/lib/faraday/rack_builder.rb
index 33ba562c3..42da63478 100644
--- a/lib/faraday/rack_builder.rb
+++ b/lib/faraday/rack_builder.rb
@@ -232,7 +232,7 @@ def adapter_set?
     end
 
     def is_adapter?(klass) # rubocop:disable Naming/PredicateName
-      klass.ancestors.include?(Faraday::Adapter)
+      klass <= Faraday::Adapter
     end
 
     ruby2_keywords def use_symbol(mod, key, *args, &block)
diff --git a/lib/faraday/request/multipart.rb b/lib/faraday/request/multipart.rb
index 25169f08b..1f96c8d96 100644
--- a/lib/faraday/request/multipart.rb
+++ b/lib/faraday/request/multipart.rb
@@ -13,7 +13,7 @@ class Multipart < UrlEncoded
       end
 
       def initialize(app = nil, options = {})
-        @app = app
+        super(app)
         @options = options
       end
 
diff --git a/lib/faraday/utils.rb b/lib/faraday/utils.rb
index 45545d150..b052f9b2f 100644
--- a/lib/faraday/utils.rb
+++ b/lib/faraday/utils.rb
@@ -28,7 +28,7 @@ class << self
 
     def escape(str)
       str.to_s.gsub(ESCAPE_RE) do |match|
-        '%' + match.unpack('H2' * match.bytesize).join('%').upcase
+        "%#{match.unpack('H2' * match.bytesize).join('%').upcase}"
       end.gsub(' ', default_space_encoding)
     end
 
@@ -89,7 +89,7 @@ def default_uri_parser=(parser)
     # the path with the query string sorted.
     def normalize_path(url)
       url = URI(url)
-      (url.path.start_with?('/') ? url.path : '/' + url.path) +
+      (url.path.start_with?('/') ? url.path : "/#{url.path}") +
         (url.query ? "?#{sort_query_params(url.query)}" : '')
     end
 
diff --git a/lib/faraday/utils/headers.rb b/lib/faraday/utils/headers.rb
index 9daef87e5..9883dc24c 100644
--- a/lib/faraday/utils/headers.rb
+++ b/lib/faraday/utils/headers.rb
@@ -105,7 +105,7 @@ def replace(other)
       end
 
       def to_hash
-        ::Hash.new.update(self)
+        {}.update(self)
       end
 
       def parse(header_string)
diff --git a/spec/faraday/request/authorization_spec.rb b/spec/faraday/request/authorization_spec.rb
index 85026d926..3f13392e6 100644
--- a/spec/faraday/request/authorization_spec.rb
+++ b/spec/faraday/request/authorization_spec.rb
@@ -56,7 +56,7 @@
     end
 
     context 'when other values are provided' do
-      let(:auth_config) { ['baz', foo: 42] }
+      let(:auth_config) { ['baz', { foo: 42 }] }
 
       it { expect(response.body).to match(/^Token /) }
       it { expect(response.body).to match(/token="baz"/) }
@@ -78,7 +78,7 @@
     end
 
     context 'when passed a string and a hash' do
-      let(:auth_config) { ['baz', foo: 42] }
+      let(:auth_config) { ['baz', { foo: 42 }] }
 
       it { expect(response.body).to eq('baz foo="42"') }
 
diff --git a/spec/support/shared_examples/request_method.rb b/spec/support/shared_examples/request_method.rb
index 917e48ca9..05257ff6f 100644
--- a/spec/support/shared_examples/request_method.rb
+++ b/spec/support/shared_examples/request_method.rb
@@ -119,7 +119,7 @@
       request_stub.with(headers: { 'Content-Type' => %r{\Amultipart/form-data} }) do |request|
         # WebMock does not support matching body for multipart/form-data requests yet :(
         # https://github.com/bblimke/webmock/issues/623
-        request.body =~ /RubyMultipartPost/
+        request.body.include?('RubyMultipartPost')
       end
       conn.public_send(http_method, '/', payload)
     end