utils/config: fix don't typo

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Reviewed-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit b3e5bcec658b8b20740c30fcd18ed3eac5ee1a3e)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

utils/config

@@ -30,7 +30,7 @@ commands:
 
 options:
 	--file config-file   .config file to change (default .config)
-	--keep-case|-k       Keep next symbols' case (dont' upper-case it)
+	--keep-case|-k       Keep next symbols' case (don't upper-case it)
 	--package|-p         Operate on package (set prefix to BR2_PACKAGE_)
 
 $myname doesn't check the validity of the .config file. This is done at next