Documentation: Spelling fixes

Signed-off-by: Horst H. von Brand <vonbrand@inf.utfsm.cl>
Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/Documentation/git-update-index.txt b/Documentation/git-update-index.txt
index d043e86..3ae6e74 100644
--- a/Documentation/git-update-index.txt
+++ b/Documentation/git-update-index.txt
@@ -40,7 +40,7 @@
 --remove::
 	If a specified file is in the index but is missing then it's
 	removed.
-	Default behaviour is to ignore removed file.
+	Default behavior is to ignore removed file.
 
 --refresh::
 	Looks at the current index and checks to see if merges or