git-clean doc: fix "without do cleaning" typo

"quit without do cleaning" is not grammatical.

Signed-off-by: Caleb Hill <chill389cc@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: chill389cc

Documentation/git-clean.txt

@@ -127,7 +127,7 @@ ask each::
 
 quit::
 
-  This lets you quit without do cleaning.
+  This lets you quit without doing any cleaning.
 
 help::