add core-docs as dependency

Author: Scott J. Miles

bower.json

@@ -5,6 +5,7 @@
     "polymer": "Polymer/polymer#master",
     "core-layout-trbl": "Polymer/core-layout-trbl#master",
     "core-ajax": "Polymer/core-ajax#master",
+    "core-docs": "Polymer/core-docs#master",
     "core-firebase": "Polymer/core-firebase#master",
     "core-icon": "Polymer/core-icon#master",
     "core-iconset": "Polymer/core-iconset#master",