add rubocop gem

Gemfile

@@ -73,8 +73,6 @@ group :development, :test do
   gem 'byebug'
   gem 'pry-byebug'
 
-  gem 'rubocop'
-
   # Access an IRB console on exception pages or by using <%= console %> in views
   gem 'web-console', '~> 2.0'
 
@@ -84,5 +82,9 @@ group :development, :test do
   gem 'rspec-rails', '~> 3.0'
 
   gem 'railroady'
+
+  gem 'rubocop', require: false
+  gem 'rubocop-checkstyle_formatter', require: false
+  gem 'rubocop-rspec', require: false
 end
 

Gemfile.lock

@@ -228,6 +228,9 @@ GEM
       powerpack (~> 0.1)
       rainbow (>= 1.99.1, < 3.0)
       ruby-progressbar (~> 1.4)
+    rubocop-checkstyle_formatter (0.2.0)
+      rubocop (>= 0.20.1)
+    rubocop-rspec (1.3.0)
     ruby-progressbar (1.7.5)
     ruby_parser (3.7.0)
       sexp_processor (~> 4.1)
@@ -326,6 +329,8 @@ DEPENDENCIES
   rgeo-geojson
   rspec-rails (~> 3.0)
   rubocop
+  rubocop-checkstyle_formatter
+  rubocop-rspec
   sass-rails (~> 5.0)
   sdoc (~> 0.4.0)
   selenium-webdriver