Revert "Remove ws dependency now managed in collaboration package"

This reverts commit dc8362cabf.

This is still needed since apm install does not install dev dependencies
of third-party modules.

package.json

@@ -109,6 +109,7 @@
     "grunt-contrib-less": "~0.6.4",
     "jasmine-focused": "~0.7.0",
     "walkdir": "0.0.7",
+    "ws": "0.4.27",
     "js-yaml": "~2.1.0"
   },
   "private": true,