Update buck version to match Gerrit master branch

Change-Id: I32829544e947e37db4dadb71d63f817546c453a5
diff --git a/buckversion b/buckversion
index f5fe016..128a75f 100644
--- a/buckversion
+++ b/buckversion
@@ -1 +1 @@
-e64a2e2ada022f81e42be750b774024469551398
+6a19cf921c107ea0f1751e4f84c639e5050e2da7
diff --git a/gerrit_plugin.bucklet b/gerrit_plugin.bucklet
index 922bd77..c8be95d 100644
--- a/gerrit_plugin.bucklet
+++ b/gerrit_plugin.bucklet
@@ -138,7 +138,7 @@
         ':%s__gwt_application' % name +
         ';cd $TMP' +
         ';zip -qr $OUT .',
-      out = '%s-static.zip' % name,
+      out = '%s-static.jar' % name,
     )
     gwt_binary(
       name = name + '__gwt_application',