fixed punctuation

Author: arthurlw

pandas/core/groupby/groupby.py

@@ -3833,7 +3833,7 @@ def expanding(
         Returns
         -------
         pandas.api.typing.ExpandingGroupby
-            An object that supports expanding transformations over each group
+            An object that supports expanding transformations over each group.
 
         See Also
         --------