Update contributing page link to latest not edge (#6149)

Signed-off-by: Charlie Egan <[email protected]>

Author: charlieegan3

CONTRIBUTING.md

@@ -2,5 +2,5 @@
 
 Thanks for your interest in contributing to the Open Policy Agent (OPA) project!
 
-Please refer to [OPA's contribution guidelines](https://www.openpolicyagent.org/docs/edge/contributing/)
+Please refer to [OPA's contribution guidelines](https://www.openpolicyagent.org/docs/latest/contributing/)
 to find out how you can help.