Bump bootsnap

When attempting to run the server on Ruby 3.0.4, it fails. Apparently,
some bug was released in Ruby 3.0.3 that affects Bootsnap. However,
Bootsnap released a workaround patch.

Error:
```
.rbenv/versions/3.0.4/lib/ruby/gems/3.0.0/gems/bootsnap-1.7.5/lib/bootsnap/compile_cache/iseq.rb:13:in `to_binary': wrong argument type false (expected Symbol) (TypeError)
```

Reference:
- Shopify/bootsnap#378

Gemfile

@@ -4,7 +4,7 @@ git_source(:github) { |_repo| "https://github.com/#{repo}.git" }
 ruby '2.7.5'
 
 gem 'autoprefixer-rails'
-gem 'bootsnap', '>= 1.4.2', require: false
+gem 'bootsnap', '>= 1.15.0', require: false
 gem 'devise'
 gem 'font-awesome-sass'
 gem 'jbuilder', '~> 2.7'

Gemfile.lock

@@ -65,8 +65,8 @@ GEM
       execjs (> 0)
     bcrypt (3.1.16)
     bindex (0.8.1)
-    bootsnap (1.7.5)
-      msgpack (~> 1.0)
+    bootsnap (1.15.0)
+      msgpack (~> 1.2)
     builder (3.2.4)
     byebug (11.1.3)
     coderay (1.1.3)
@@ -108,7 +108,7 @@ GEM
     minitest (5.15.0)
     minitest-ci (3.4.0)
       minitest (>= 5.0.6)
-    msgpack (1.4.2)
+    msgpack (1.6.0)
     nio4r (2.5.8)
     nokogiri (1.13.6-arm64-darwin)
       racc (~> 1.4)
@@ -255,7 +255,7 @@ PLATFORMS
 
 DEPENDENCIES
   autoprefixer-rails
-  bootsnap (>= 1.4.2)
+  bootsnap (>= 1.15.0)
   devise
   dotenv-rails
   font-awesome-sass