Add RuboCop

.rubocop.yml

@@ -0,0 +1,15 @@
+AllCops:
+  TargetRubyVersion: 2.3
+  DisplayCopNames: true
+
+Layout/AccessModifierIndentation:
+  EnforcedStyle: outdent
+
+Metrics/LineLength:
+  Max: 120
+
+Style/TrailingCommaInArguments:
+  EnforcedStyleForMultiline: comma
+
+Style/TrailingCommaInLiteral:
+  EnforcedStyleForMultiline: comma

Gemfile

@@ -3,3 +3,7 @@
 source 'https://rubygems.org'
 
 gem 'tox', path: '../tox.rb'
+
+group :development, :test do
+  gem 'rubocop', '~> 0.49.1'
+end

Gemfile.lock

@@ -6,11 +6,29 @@ PATH
 GEM
   remote: https://rubygems.org/
   specs:
+    ast (2.3.0)
+    parallel (1.11.2)
+    parser (2.4.0.0)
+      ast (~> 2.2)
+    powerpack (0.1.1)
+    rainbow (2.2.2)
+      rake
+    rake (12.0.0)
+    rubocop (0.49.1)
+      parallel (~> 1.10)
+      parser (>= 2.3.3.1, < 3.0)
+      powerpack (~> 0.1)
+      rainbow (>= 1.99.1, < 3.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (~> 1.0, >= 1.0.1)
+    ruby-progressbar (1.8.1)
+    unicode-display_width (1.3.0)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
+  rubocop (~> 0.49.1)
   tox!
 
 BUNDLED WITH

Rakefile

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+task default: :lint
+
+task lint: :rubocop
+
+task fix: 'rubocop:auto_correct'
+
+begin
+  require 'rubocop/rake_task'
+  RuboCop::RakeTask.new
+rescue LoadError
+  nil
+end