Apply automatic rubocop fixes

db/migrate/20180815115351_remove_event_indices.rb

@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 class RemoveEventIndices < ActiveRecord::Migration[4.2]
   def change
-    remove_index :events, [:user_type, :user_id]
+    remove_index :events, %i[user_type user_id]
     remove_index :events, :exercise_id
     remove_index :events, :file_id
   end