Add gerrit-*_pom.xml.asc files from deployment to .gitignore

As these get generated by the tools/maven/api.sh {war_}deploy commands.

Change-Id: Ia284e3ac80fd0d89593bcf8be80b56d083828f9f
diff --git a/.gitignore b/.gitignore
index 94d78c4..fb53fc6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -46,5 +46,6 @@
 !/plugins/webhooks
 /test_site
 /tools/format
+/tools/maven/gerrit-*_pom.xml.asc
 /tools/node_tools
 /tools/polygerrit-updater