Added changes entry for group_sort fix

Author: ricellis

CHANGES.rst

@@ -16,6 +16,7 @@
   the 2.0.0 behaviour use: ``adapter=Replay429Adapter(retries=10, initialBackoff=0.25)``. If ``retries`` or
   ``initialBackoff`` are not specified they will default to 3 retries and a 0.25 s initial backoff.
 - [FIX] ``415 Client Error: Unsupported Media Type`` when using keys with ``db.all_docs``.
+- [FIX] Allowed strings as well as lists for search ``group_sort`` arguments.
 
 2.0.3 (2016-06-03)
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