Allow gerrit-verifiers to submit plugin changes

This makes the permissions more consistent with gerrit itself.
diff --git a/project.config b/project.config
index 930152c..a2339e7 100644
--- a/project.config
+++ b/project.config
@@ -10,6 +10,7 @@
 	label-Verified = -1..+1 group Project Owners
 	label-Verified = -1..+1 group gerrit-verifiers
 	submit = group Project Owners
+	submit = group gerrit-verifiers
 [access "refs/tags/*"]
 	createTag = group Project Owners
 	createTag = group gerrit-release-creators