[Fix rubocop#790] Make Style/HashExcept aware of TargetRubyVersion: 2.x

Fixes rubocop#790.

This PR makes `Style/HashExcept` aware of TargetRubyVersion: 2.x
because Rails has `Hash#except`.
So Ruby version is irrelevant when used in Rails.

Author: koic

changelog/new_make_style_hash_except_aware_of_target_ruby_version_2_x.md

@@ -0,0 +1 @@
+* [#790](https://github.com/rubocop/rubocop-rails/issues/790): Make `Style/HashExcept` aware of TargetRubyVersion: 2.x because Rails has `Hash#except`. ([@koic][])

lib/rubocop-rails.rb

@@ -14,6 +14,8 @@
 
 require_relative 'rubocop/cop/rails_cops'
 
+RuboCop::Cop::Style::HashExcept.minimum_target_ruby_version(2.0)
+
 RuboCop::Cop::Style::MethodCallWithArgsParentheses.singleton_class.prepend(
   Module.new do
     def autocorrect_incompatible_with

spec/rubocop/cli/autocorrect_spec.rb

@@ -40,4 +40,20 @@
       self&.bar&.baz
     RUBY
   end
+
+  it 'corrects `Style/HashExcept` with `TargetRubyVersion: 2.0`' do
+    create_file('.rubocop.yml', <<~YAML)
+      AllCops:
+        TargetRubyVersion: 2.0
+    YAML
+
+    create_file('example.rb', <<~RUBY)
+      {foo: 1, bar: 2, baz: 3}.reject {|k, v| k == :bar }
+    RUBY
+
+    expect(cli.run(['-a', '--only', 'Style/HashExcept'])).to eq(0)
+    expect(File.read('example.rb')).to eq(<<~RUBY)
+      {foo: 1, bar: 2, baz: 3}.except(:bar)
+    RUBY
+  end
 end