talksapp: fail fast if GitHub metadata is missing
talksapp: fail fast if GitHub metadata is missing

This will avoid problems where people deploy without the credentials.

Change-Id: I816e084df823e2ae83c823724534e7c0640b6e88
Reviewed-on: https://go-review.googlesource.com/28642
Reviewed-by: Chris Broadfoot <0c2851a4f8ab4aa5606e69c0757771dd13dbe686@golang.org>

golang/gddo,segmentio/gddo,segmentio/gddo,golang/gddo,segmentio/gddo,segmentio/gddo,golang/gddo,golang/gddo