git-cherry-pick.txt: correct a small typo

Most of the document mentions `behavior` instead of the British
variation, `behaviour`. This change makes it consistent.

Signed-off-by: Pablo Santiago Blum de Aguiar <scorphus@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: scorphus

Documentation/git-cherry-pick.txt

@@ -125,7 +125,7 @@ effect to your index in a row.
 
 --allow-empty-message::
 	By default, cherry-picking a commit with an empty message will fail.
-	This option overrides that behaviour, allowing commits with empty
+	This option overrides that behavior, allowing commits with empty
 	messages to be cherry picked.
 
 --keep-redundant-commits::