Bump to 1.9.0-2

Merge pull request #143 from Fokko/update-to-airflow-19

Update to Apache Airflow 1.9

Merge pull request #114 from puckel/v1.8.2

Bump to 1.8.2

Update to python 3

Merge pull request #83 from puckel/1.8.1

Bump to 1.8.1

Merge pull request #74 from puckel/v1.8.0

v1.8.0

Bump to 1.7.1.3-7

Merge pull request #52 from darkk/master

Scheduler restart speedup & minor fixes

Set external images version

Update airflow.cfg