Apply automatic rubocop fixes

db/migrate/20170202170437_create_remote_evaluation_mappings.rb

@@ -1,11 +1,13 @@
+# frozen_string_literal: true
+
 class CreateRemoteEvaluationMappings < ActiveRecord::Migration[4.2]
   def change
     create_table :remote_evaluation_mappings do |t|
-      t.integer   "user_id",          null: false
-      t.integer   "exercise_id",      null: false
-      t.string    "validation_token",  null: false
-      t.datetime  "created_at"
-      t.datetime  "updated_at"
+      t.integer   'user_id',          null: false
+      t.integer   'exercise_id',      null: false
+      t.string    'validation_token', null: false
+      t.datetime  'created_at'
+      t.datetime  'updated_at'
     end
   end
-end
+end