Add Gerrit-PluginName in BUCK file

Change-Id: I18130bf5c45cee2f93ba05f03299b3433a34d2af
diff --git a/BUCK b/BUCK
index 361ed93..b7356f2 100644
--- a/BUCK
+++ b/BUCK
@@ -2,6 +2,7 @@
   name = 'singleusergroup',
   srcs = glob(['src/main/java/**/*.java']),
   manifest_entries = [
+    'Gerrit-PluginName: singleusergroup',
     'Gerrit-Module: com.googlesource.gerrit.plugins.singleusergroup.SingleUserGroup$Module',
   ],
 )