docs: update PubSubClient link in README

Author: cziter15

README.md

@@ -244,5 +244,5 @@ This design is highly flexible. For example, you can trigger a failure (`return
 
 #### 🔡 Libraries
 
-- [PubSubClient](https://github.com/cziter15/pubsubclient3) originally developed by @hmueller01 and @knolleary
+- [PubSubClient](https://github.com/cziter15/pubsubclient) originally developed @knolleary
 - [arduinoWebSockets](https://github.com/cziter15/arduinoWebSockets) originally developed by @Links2004