Avoid 1 use of keyword hackery (#1211)

lib/faraday/dependency_loader.rb

@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 
-require 'ruby2_keywords'
-
 module Faraday
   # DependencyLoader helps Faraday adapters and middleware load dependencies.
   module DependencyLoader
@@ -15,7 +13,7 @@ def dependency(lib = nil)
       self.load_error = e
     end
 
-    ruby2_keywords def new(*)
+    def new(*)
       unless loaded?
         raise "missing dependency for #{self}: #{load_error.message}"
       end