Lint with rubocop-jekyll

.rubocop.yml

@@ -1,14 +1,14 @@
+require: rubocop-jekyll
+
 inherit_gem:
-  jekyll: .rubocop.yml
+  rubocop-jekyll: .rubocop.yml
 
 AllCops:
-  TargetRubyVersion: 2.3
-  Include:
-    - report
-    - github/jwt
+  TargetRubyVersion: 2.5
   Exclude:
     - sites/**/*
     - vendor/**/*
+    - Gemfile
 
 Jekyll/NoPutsAllowed:
   Enabled: false

.travis.yml

@@ -1,5 +1,5 @@
 language: ruby
-rvm: 2.4
+rvm: 2.5
 cache: bundler
 
 branches:
@@ -16,6 +16,6 @@ before_script:
 matrix:
   include:
   - name: Rubocop
-    script: bundle exec rubocop -D
+    script: bundle exec rubocop -S -D -E
   - name: bench
     script: ./bench

Gemfile

@@ -1,11 +1,13 @@
+# frozen_string_literal: true
+
 source "https://rubygems.org"
 
 repo = ENV.fetch("REPO", "https://github.com/jekyll/jekyll.git")
 
 if ENV["REF"]
   gem "jekyll", git: repo, ref: ENV["REF"]
 elsif ENV["PR"]
-  gem "jekyll", git: repo, ref: "refs/pull/#{ENV['PR']}/head"
+  gem "jekyll", git: repo, ref: "refs/pull/#{ENV["PR"]}/head"
 else
   gem "jekyll", git: repo, branch: "master"
 end
@@ -63,5 +65,5 @@ gem "redcarpet"
 gem "uswds-jekyll"
 
 group :dev do
-  gem "rubocop", "~> 0.66.0"
+  gem "rubocop-jekyll", "~> 0.11"
 end