Downgrade angularjs-scroll-glue (#874)
This was already done in 06f1d5c1e158a50cd41f69cc3ed01e27206fad1b, but
I accidentally re-upgraded. Version 2.2.0 causes laggy UI behavior when
switching chats.
This time the exact version is pinned, then it should be obvious that
there's a reason for that. Unfortunately comments cannot be added to
JSON files...
Fixes #870