[wip] Update 0.34.0

[dpordomingo]

fix #276

• Update from 0.34.0rc1 to 0.34.0
• Link to release in mailing list: https://lists.apache.org/thread.html/da4cf476982d4090b404de484bb092a9b1bb971b5633a57a4a55a874@%3Cdev.superset.apache.org%3E
• Common ancestor between versions: sha-1 a04fad858644466219b7ea399aead110cb8ea655 (not from mailing list, but from git merge-base 0.34.0rc1 0.34.0)
• Last split commit: sha-1 a04fad858644466219b7ea399aead110cb8ea655

Performed checks

• [x] I updated Makefile with the new SUPERSET_VERSION
• [x] I updated the CHANGELOG file
• Migrations:
  • [ ] I merged migrations
  • [x] No migration merge was needed
• I checked the config files (and ported if needed):
  • superset/contib/docker
  • [ ] changes merged
  • [x] nothing to be merged
  • superset/superset/config.py
  • [ ] changes merged
  • [x] nothing to be merged
  • superset/.travis.yml
  • [ ] changes merged
  • [x] nothing to be merged
• [x] Tested the upgrade building & checking it with src-d/sourced-ce

notes

0.34.0rc1, its common ancestor with 0.34.0, and the split commit are equals because 0.34.0 release branch was created from 0.34.0rc1. Also, there is no revert commit to merge because there is no changes in 0.34.0rc1 which are not in 0.34.0.

[smacker]

I think we decided to close this one and update to 0.34.1 instead as soon as it's released. (the vote process has started already https://lists.apache.org/thread.html/a7738227137db736497b2dda41fa266504bf889bc47941dab4d1abf0@%3Cdev.superset.apache.org%3E )

[dpordomingo]

Yes, forgot to close it. Done