Add Gerrit-PluginName in BUCK file

Change-Id: I9e64b8d5d873075bf3310d7acbfded40703c418e
diff --git a/BUCK b/BUCK
index 1d6a76d..a770d7d 100644
--- a/BUCK
+++ b/BUCK
@@ -2,4 +2,7 @@
   name = 'commit-message-length-validator',
   srcs = glob(['src/main/java/**/*.java']),
   resources = glob(['src/main/resources/**/*']),
+  manifest_entries = [
+    'Gerrit-PluginName: commit-message-length-validator',
+  ],
 )