Fix minor formatting issue

guides/source/threading_and_code_execution.md

@@ -186,7 +186,7 @@ code to execute each job as it comes off the queue.
 
 Action Cable uses the Executor instead: because a Cable connection is linked to
 a specific instance of a class, it's not possible to reload for every arriving
-websocket message. Only the message handler is wrapped, though; a long-running
+WebSocket message. Only the message handler is wrapped, though; a long-running
 Cable connection does not prevent a reload that's triggered by a new incoming
 request or job. Instead, Action Cable uses the Reloader's `before_class_unload`
 callback to disconnect all its connections. When the client automatically