bash prompt: remove a redundant 'git diff' option

To get the dirty state indicator __git_ps1() runs 'git diff' with
'--quiet --exit-code' options.  '--quiet' already implies
'--exit-code', so the latter is unnecessary and can be removed.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Jeff King <peff@peff.net>

contrib/completion/git-prompt.sh

@@ -476,7 +476,7 @@ __git_ps1 ()
 		if [ -n "${GIT_PS1_SHOWDIRTYSTATE-}" ] &&
 		   [ "$(git config --bool bash.showDirtyState)" != "false" ]
 		then
-			git diff --no-ext-diff --quiet --exit-code || w="*"
+			git diff --no-ext-diff --quiet || w="*"
 			if [ -n "$short_sha" ]; then
 				git diff-index --cached --quiet HEAD -- || i="+"
 			else