v3.13.1

This version contains a fix for the newly added orchestration feature. Instead of relying on the EXPECTED_PROJECTS env variable, we're exposing a separate API endpoint, https://happo.io/docs/api#Create%20an%20orchestration%20job, that you can use the combine multiple projects in a single build status.

Technically, removing EXPECTED_PROJECTS is a breaking change, but since no usage has been reported for this feature we feel pretty confident this is a non-breaking change.