Add tags to git ignore

Signed-off-by: Michael Xu <mxu@pivotal.io>

Author: Difan Zhao

.gitignore

@@ -14,6 +14,7 @@ dev_releases/
 releases/**/*.tgz
 releases/*.tgz
 src/bosh-dns/acceptance_tests/linux/override_nameserver/disabled/dns-creds.yml
+tags
 
 # Golang
 /bin/