Add Style enforcer (via Rubocop)

It will fail the build, but as it is currently,
most of the cops are 'todos'. Great for new contributors.. :)

test/action_controller/serialization_test.rb

@@ -1,4 +1,3 @@
-
 require 'test_helper'
 
 module ActionController
@@ -189,7 +188,7 @@ module ActionController
       def test_render_array_using_custom_root
         get :render_array_using_custom_root
 
-        expected =  {custom_roots: [{name: "Name 1", description: "Description 1"}]}
+        expected = {custom_roots: [{name: "Name 1", description: "Description 1"}]}
         assert_equal 'application/json', @response.content_type
         assert_equal expected.to_json, @response.body
       end
@@ -197,7 +196,7 @@ module ActionController
       def test_render_array_that_is_empty_using_custom_root
         get :render_array_that_is_empty_using_custom_root
 
-        expected =  {custom_roots: []}
+        expected = {custom_roots: []}
         assert_equal 'application/json', @response.content_type
         assert_equal expected.to_json, @response.body
       end
@@ -205,7 +204,7 @@ module ActionController
       def test_render_object_using_custom_root
         get :render_object_using_custom_root
 
-        expected =  {custom_root: {name: "Name 1", description: "Description 1"}}
+        expected = {custom_root: {name: 'Name 1', description: 'Description 1'}}
         assert_equal 'application/json', @response.content_type
         assert_equal expected.to_json, @response.body
       end

test/fixtures/poro.rb

@@ -83,7 +83,7 @@ Location = Class.new(Model)
 Place    = Class.new(Model)
 Tag      = Class.new(Model)
 VirtualValue = Class.new(Model)
-Comment  = Class.new(Model) do
+Comment = Class.new(Model) do
   # Uses a custom non-time-based cache key
   def cache_key
     "#{self.class.name.downcase}/#{self.id}"

test/serializers/serializer_for_test.rb

@@ -26,7 +26,7 @@ module ActiveModel
         end
       end
 
-      class SerializerTest <  Minitest::Test
+      class SerializerTest < Minitest::Test
         class MyProfile < Profile
         end
         class CustomProfile

test/support/stream_capture.rb

@@ -29,7 +29,7 @@ rescue LoadError
         def capture(stream)
           stream = stream.to_s
           captured_stream = Tempfile.new(stream)
-          stream_io = eval("$#{stream}")
+          stream_io = eval("$#{stream}") # rubocop:disable Lint/Eval
           origin_stream = stream_io.dup
           stream_io.reopen(captured_stream)