Explicitly join the fields array to a comma-delimited string.
Explicitly join the fields array to a comma-delimited string.

With https://github.com/meteor/meteor/pull/8261 merged, arrays are no longer concatenated (with commas) into a string during `HTTP.call` requests so we need to specify the exact behavior we want. Any previous behavior of this type was purely accidental.

The definition of this field in Facebook's API is that it should be a comma-separated field:

https://developers.facebook.com/docs/graph-api/using-graph-api

Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor