talksapp: fix environment variable access
talksapp: fix environment variable access

Environment variables in Go are not accessible until a first request
arrives.

https://cloud.google.com/appengine/docs/go/config/appconfig#Go_app_yaml_Defining_environment_variables

The previous code was accessing them at variable declaration time,
obtaining empty values and causing authentication issues.

Change-Id: Id64e7c93453f9aded04d935cf49eccba0f9a6923

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