Revert "Drop support for EOL'd Ruby 2.6"

This reverts commit aa336d6.

Author: amatsuda

.github/workflows/main.yml

@@ -10,6 +10,7 @@ jobs:
 
       matrix:
         ruby-version:
+          - '2.6'
           - '2.7'
           - '3.0'
           - '3.1'

.rubocop.yml

@@ -6,7 +6,7 @@ require:
 AllCops:
   DisplayCopNames: true
   NewCops: enable
-  TargetRubyVersion: 2.7
+  TargetRubyVersion: 2.6
 
 Bundler/DuplicatedGem:
   Enabled: false

Gemfile

@@ -16,7 +16,7 @@ group :test do
 end
 
 group :development do
-  gem "rubocop"
+  gem "rubocop", "~> 1.50.2"
   gem "rubocop-minitest"
   gem "rubocop-performance"
   gem "rubocop-rake"

Gemfile.lock

@@ -21,7 +21,6 @@ GEM
     execjs (2.9.1)
     json (2.7.1)
     json (2.7.1-java)
-    language_server-protocol (3.17.0.3)
     minitest (5.20.0)
     parallel (1.24.0)
     parser (3.2.2.4)
@@ -35,15 +34,14 @@ GEM
     regexp_parser (2.8.3)
     rexml (3.3.6)
       strscan
-    rubocop (1.59.0)
+    rubocop (1.50.2)
       json (~> 2.3)
-      language_server-protocol (>= 3.17.0)
       parallel (~> 1.10)
-      parser (>= 3.2.2.4)
+      parser (>= 3.2.0.0)
       rainbow (>= 2.2.2, < 4.0)
       regexp_parser (>= 1.8, < 3.0)
       rexml (>= 3.2.5, < 4.0)
-      rubocop-ast (>= 1.30.0, < 2.0)
+      rubocop-ast (>= 1.28.0, < 2.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 2.4.0, < 3.0)
     rubocop-ast (1.30.0)
@@ -77,7 +75,7 @@ DEPENDENCIES
   bundler (~> 2.4.0)
   minitest
   rake (>= 11)
-  rubocop
+  rubocop (~> 1.50.2)
   rubocop-minitest
   rubocop-performance
   rubocop-rake

simplecov-html.gemspec

@@ -14,7 +14,7 @@ Gem::Specification.new do |gem|
   gem.summary     = gem.description
   gem.license     = "MIT"
 
-  gem.required_ruby_version = ">= 2.7"
+  gem.required_ruby_version = ">= 2.6"
 
   gem.files = Dir.chdir(__dir__) do
     `git ls-files -z`.split("\x0").reject do |f|