.gitignore: ignore qmp-commands.txt

This file is moved out from QMP/ to BUILD dir, change the ignore file
too.
Signed-off-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

.gitignore

@@ -44,7 +44,7 @@ qemu-ga
 qemu-bridge-helper
 qemu-monitor.texi
 vscclient
-QMP/qmp-commands.txt
+qmp-commands.txt
 test-bitops
 test-coroutine
 test-int128