Drop the support of Ruby 2.2

Since github flow fails to install bundler in Ruby 2.2.

The error message:
  Bundler 2 requires Ruby 2.3+, using Bundler 1 on Ruby <= 2.2
  /opt/hostedtoolcache/Ruby/2.2.10/x64/bin/gem install bundler -v ~> 1.0
  ERROR:  While executing gem ... (RuntimeError)
      Marshal.load reentered at marshal_load
  Took   0.30 seconds
Error: The process '/opt/hostedtoolcache/Ruby/2.2.10/x64/bin/gem' failed with exit code 1

.github/workflows/ruby.yml

@@ -20,7 +20,7 @@ jobs:
       fail-fast: false
       matrix:
         ruby:
-          - 2.2
+          - 2.3
           - 2.6
           - 2.7
           - 3.0
@@ -62,11 +62,11 @@ jobs:
           - gemfile: 5.2.gemfile
             ruby: 3.1
           - gemfile: 6.0.gemfile
-            ruby: 2.2
+            ruby: 2.3
           - gemfile: 6.1.gemfile
-            ruby: 2.2
+            ruby: 2.3
           - gemfile: 7.0.gemfile
-            ruby: 2.2
+            ruby: 2.3
           - gemfile: 7.0.gemfile
             ruby: 2.6
     env:

README.md

@@ -7,7 +7,7 @@
 [![Test Coverage](https://codeclimate.com/github/khiav223577/rails_compatibility/badges/coverage.svg)](https://codeclimate.com/github/khiav223577/rails_compatibility/coverage)
 
 ## Supports
-- Ruby 2.2 ~ 2.7, 3.0 ~ 3.1
+- Ruby 2.3 ~ 2.7, 3.0 ~ 3.1
 - Rails 3.2, 4.2, 5.0, 5.1, 5.2, 6.0, 6.1, 7.0
 
 ## Installation