deps: Drop Ruby v2.6 / Require Ruby v2.7+ (#180)

* deps: Require Ruby v2.7+

* chore: TargetRubyVersion: 2.7

Author: toshimaru

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
   test:
     strategy:
       matrix:
-        ruby: ["2.6", "2.7", "3.0", "3.1", "3.2", "3.3"]
+        ruby: ["2.7", "3.0", "3.1", "3.2", "3.3"]
         gemfile:
           - gemfiles/jekyll_3.9.gemfile
           - gemfiles/jekyll_4.0.gemfile

.rubocop.yml

@@ -1,5 +1,5 @@
 AllCops:
-  TargetRubyVersion: 2.6
+  TargetRubyVersion: 2.7
   NewCops: enable
   Exclude:
     - "*.gemspec"

jekyll-toc.gemspec

@@ -26,7 +26,7 @@ Gem::Specification.new do |spec|
     end
   end
 
-  spec.required_ruby_version = '>= 2.6'
+  spec.required_ruby_version = '>= 2.7'
 
   spec.add_dependency 'jekyll', '>= 3.9'
   spec.add_dependency 'nokogiri', '~> 1.12'