compat-wireless: Add entry for master-tag in .gitignore

master-tag wasn't mentioned in .gitignore, despite it being manufactured by scripts/admin-update.sh.

---
 .gitignore |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

index 6b78bab..b6a26d3 100644
@@ -4,6 +4,7 @@ net
 *~
 git-describe
 compat-release
+master-tag
 .compat_autoconf*
 .config.md5
 .config.mk_md5sum.txt