Pass release channel when checking for update
Pass release channel when checking for update

Summary: Retrieve updated version in accordance to the currently selected release channel. Also changed message for "insiders" channel - removed mention of fbsource pinning.

Reviewed By: mweststrate

Differential Revision: D26011703

fbshipit-source-id: 7f3396e89db047cb24b4e00b224f79ca0fd64327

facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper