Update cookbook plugin revision

- Update GWT to 2.6.1 to match version used in core Gerrit

Change-Id: Idcefc11b9228d2c26fcff31261f9f8f1397ade02
diff --git a/plugins/cookbook-plugin b/plugins/cookbook-plugin
index f95eb05..679a135 160000
--- a/plugins/cookbook-plugin
+++ b/plugins/cookbook-plugin
@@ -1 +1 @@
-Subproject commit f95eb05f758fc62726b2938b26f0e6b3f023d02b
+Subproject commit 679a1356ec20f7570246af77fa4e4c6f10ed3a42