[docs] Changelog had wrong ref link

Changelog

@@ -8,9 +8,9 @@ This document contains change notes for bugfix releases in the 3.1.x series
 (Cipater), please see :ref:`whatsnew-3.1` for an overview of what's
 new in Celery 3.1.
 
-.. _version-3.0.0:
+.. _version-3.1.0:
 
-3.0.0
+3.1.0
 =====
 :release-date: TBA
 :state: FROZEN

docs/history/changelog-3.0.rst

@@ -1,4 +1,4 @@
-.. _changelog:
+.. _changelog-3.0:
 
 ================
  Change history
@@ -160,7 +160,7 @@ If you're looking for versions prior to 3.0.x you should go to :ref:`history`.
 
 - MongoDB Backend: The :setting:`MONGODB_BACKEND_SETTINGS` setting
   now accepts a ``option`` key that lets you forward arbitrary kwargs
-  to the underlying ``pymongo.Connection` object (Issue #1015).
+  to the underlying ``pymongo.Connection`` object (Issue #1015).
 
 - Beat: The daily backend cleanup task is no longer enabled
   for result backends that support automatic result expiration (Issue #1031).