Add sha1 for the Gerrit plugin api dependency

Change-Id: I6da9dd3c1f0d8b5f510f247bf014265d644bc949

lib/gerrit/BUCK

diff --git a/lib/gerrit/BUCK b/lib/gerrit/BUCK
index afef11a..4179430 100644
--- a/lib/gerrit/BUCK
+++ b/lib/gerrit/BUCK
@@ -6,6 +6,7 @@
 maven_jar(
   name = 'plugin-api',
   id = 'com.google.gerrit:gerrit-plugin-api:' + VER,
+  sha1 = '621012e67c64774d9743d7c7c8b0cae0998fae0d',
   attach_source = False,
   repository = REPO,
   license = 'Apache2.0',