Fix failing webhooks for non-organization based events.
Fix failing webhooks for non-organization based events.

mrrrgn/taskcluster-github,mythmon/taskcluster-github,petemoore/taskcluster-github,mythmon/taskcluster-github,mrrrgn/taskcluster-github,rail/taskcluster-github,taskcluster/taskcluster-github,petemoore/taskcluster-github,rail/taskcluster-github