rubocop fixes

Gemfile

@@ -1,4 +1,6 @@
-source "https://rubygems.org"
+# frozen_string_literal: true
+
+source 'https://rubygems.org'
 # Hello! This is where you manage which Jekyll version is used to run.
 # When you want to use a different version, change it below, save the
 # file and run `bundle install`. Run Jekyll with `bundle exec`, like so:
@@ -7,28 +9,27 @@ source "https://rubygems.org"
 #
 # This will help ensure the proper Jekyll version is running.
 # Happy Jekylling!
-gem "jekyll", "~> 4.2.0"
+gem 'jekyll', '~> 4.2.0'
 # This is the default theme for new Jekyll sites. You may change this to anything you like.
 # If you want to use GitHub Pages, remove the "gem "jekyll"" above and
 # uncomment the line below. To upgrade, run `bundle update github-pages`.
 # gem "github-pages", group: :jekyll_plugins
 # If you have any plugins, put them here!
 group :jekyll_plugins do
-  gem "jekyll-feed", git: "https://github.com/hyphacoop/jekyll-feed"
-  gem "jekyll-last-modified-at", "~> 1.3"
+  gem 'jekyll-feed', git: 'https://github.com/hyphacoop/jekyll-feed'
+  gem 'jekyll-last-modified-at', '~> 1.3'
 end
 
 # Windows and JRuby does not include zoneinfo files, so bundle the tzinfo-data gem
 # and associated library.
 platforms :mingw, :x64_mingw, :mswin, :jruby do
-  gem "tzinfo", "~> 1.2"
-  gem "tzinfo-data"
+  gem 'tzinfo', '~> 1.2'
+  gem 'tzinfo-data'
 end
 
 # Performance-booster for watching directories on Windows
-gem "wdm", "~> 0.1.1", :platforms => [:mingw, :x64_mingw, :mswin]
+gem 'wdm', '~> 0.1.1', platforms: %i[mingw x64_mingw mswin]
 
+gem 'html-proofer', '~> 3.18'
 
-gem "html-proofer", "~> 3.18"
-
-gem "rake", "~> 13.0"
+gem 'rake', '~> 13.0'