adhere to rubocop guidelines

app/channels/application_cable/channel.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ApplicationCable
   class Channel < ActionCable::Channel::Base
   end

app/channels/application_cable/connection.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ApplicationCable
   class Connection < ActionCable::Connection::Base
   end

app/channels/waiting_channel.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class WaitingChannel < ApplicationCable::Channel
   def subscribed
     stream_from "#{params[:uid]}_waiting_channel"