v0.39.1: Release pubsub 0.39.1 (#6949)

12-17-2018 16:57 PST

Implementation Changes

• Initialize StreamingPullFuture._cancelled as True. (#6901)
• Import iam.policy from google.api_core. (#6741)

Documentation

• Document Python 2 deprecation (#6910)
• Emphasize that returned futures may differ from stdlib futures. (#6875)

Internal / Testing Changes

• Add baseline for synth.metadata
• Update noxfile.
• blacken all gen'd libs (#6792)
• omit local deps (#6701)
• Run black at end of synth.py (#6698)
• Run Black on Generated libraries (#6666)
• Add templates for flake8, coveragerc, noxfile, and black. (#6642)