v1.2.0

Changed

• Run pep8 and docs in tox with python3.
• Use black https://pypi.org/project/black/ for code formatting.
• Update tox to return error if there are uncommitted schema changes.

Fixed

• Warn users when there is a loop and no start task identified. (bug fix)
• Lock global variables during initialization to make them thread safe. (bug fix)
• Workflow stuck in running if one or more items failed in a with items task. (bug fix)
• Fix use case where a failed with items task is run again if the task is in a cycle. (bug fix)