t5503: fix typo

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5503-tagfollow.sh

@@ -4,7 +4,7 @@ test_description='test automatic tag following'
 
 . ./test-lib.sh
 
-if !test_have_prereq NOT_MINGW; then
+if ! test_have_prereq NOT_MINGW; then
 	say "GIT_DEBUG_SEND_PACK not supported - skipping tests"
 fi