Add a note about missing break in switch statement.

[ci skip]

lib/Predis/PubSub/PubSubContext.php

@@ -115,6 +115,8 @@ class PubSubContext extends AbstractPubSubContext
                 if ($response[2] === 0) {
                     $this->invalidate();
                 }
+                // The missing break here is intentional as we must process
+                // subscriptions and unsubscriptions as standard messages.
 
             case self::MESSAGE:
                 return (object) array(