updated link to new github user (django-nonrel)

Author: Mark Unsworth

AUTHORS.rst

@@ -23,4 +23,4 @@ Contributions by
 * Brandon Pedersen (https://github.com/bpedman)
 
 (For an up-to-date list of contributors, see
-https://github.com/django-mongodb-engine/mongodb-engine/contributors.)
+https://github.com/django-nonrel/mongodb-engine/contributors.)