doc: Fix badge URLs.

Author: freezy

README.md

@@ -1,6 +1,6 @@
 # URP for Visual Pinball Engine
 
-[![UPM Package](https://img.shields.io/npm/v/org.visualpinball.engine.unity?label=org.visualpinball.engine.unity&registry_uri=https://registry.visualpinball.org&color=%2333cf57&logo=unity&style=flat)](https://registry.visualpinball.org/-/web/detail/org.visualpinball.engine.unity.urp)
+[![UPM Package](https://img.shields.io/npm/v/org.visualpinball.engine.unity.urp?label=org.visualpinball.engine.unity.urp&registry_uri=https://registry.visualpinball.org&color=%2333cf57&logo=unity&style=flat)](https://registry.visualpinball.org/-/web/detail/org.visualpinball.engine.unity.urp)
 
 *Universal Render Pipeline support for the Visual Pinball Engine.*