Fix docstring formatting issue in aggregate module

Author: sadielbartholomew

cf/aggregate.py

@@ -1831,7 +1831,7 @@ def promote_to_auxiliary_coordinate(self, properties):
         construct that spans a new independent size 1 domain axis of
         the field, and the property is deleted.
 
-         ... versionadded:: 3.15.0
+        .. versionadded:: 3.15.0
 
         :Parameters:
 
@@ -1890,7 +1890,7 @@ def promote_to_field_ancillary(self, properties):
         If a domain construct is being aggregated then it is always
         returned unchanged.
 
-         ... versionadded:: 3.15.0
+        .. versionadded:: 3.15.0
 
         :Parameters: