Support Parser::Ruby31

Parser gem has been started development for Ruby 3.1 (edge Ruby).
whitequark/parser#792

This PR supports `Parser::Ruby31`, the early adapters will be able to try
edge Ruby with RuboCop.

And this PR update to require Parser 3.0.1.1 or higher, which contains
`Parser::Ruby31`.
https://github.com/whitequark/parser/blob/master/CHANGELOG.md#v3011-2021-05-02

changelog/new_support_ruby_3_1_parser.md

@@ -0,0 +1 @@
+* [#182](https://github.com/rubocop-hq/rubocop-ast/pull/182): Support `Parser::Ruby31` for Ruby 3.1 parser (experimental). ([@koic][])

lib/rubocop/ast/processed_source.rb

@@ -236,6 +236,9 @@ def parser_class(ruby_version)
         when 2.8, 3.0
           require 'parser/ruby30'
           Parser::Ruby30
+        when 3.1
+          require 'parser/ruby31'
+          Parser::Ruby31
         else
           raise ArgumentError,
                 "RuboCop found unknown Ruby version: #{ruby_version.inspect}"

rubocop-ast.gemspec

@@ -32,7 +32,7 @@ Gem::Specification.new do |s|
     'bug_tracker_uri' => 'https://github.com/rubocop-hq/rubocop-ast/issues'
   }
 
-  s.add_runtime_dependency('parser', '>= 2.7.1.5')
+  s.add_runtime_dependency('parser', '>= 3.0.1.1')
 
   s.add_development_dependency('bundler', '>= 1.15.0', '< 3.0')
 

spec/spec_helper.rb

@@ -43,6 +43,10 @@
   let(:ruby_version) { 3.0 }
 end
 
+RSpec.shared_context 'ruby 3.1', :ruby31 do
+  let(:ruby_version) { 3.1 }
+end
+
 # ...
 module DefaultRubyVersion
   extend RSpec::SharedContext