DOC: Fix typo (pandas-dev#37636)

"columns(s)" sounded odd, I believe it was supposed to be just "column(s)".

Author: MicaelJarniac

pandas/core/frame.py

@@ -6449,7 +6449,7 @@ def update(
         See Also
         --------
         dict.update : Similar method for dictionaries.
-        DataFrame.merge : For column(s)-on-columns(s) operations.
+        DataFrame.merge : For column(s)-on-column(s) operations.
 
         Examples
         --------
@@ -7985,7 +7985,7 @@ def join(
 
         See Also
         --------
-        DataFrame.merge : For column(s)-on-columns(s) operations.
+        DataFrame.merge : For column(s)-on-column(s) operations.
 
         Notes
         -----