Upgrade package development requirements to match upstream Girder
Upgrade package development requirements to match upstream Girder

Coverage changes at:
http://coverage.readthedocs.io/en/coverage-4.1/changes.html#version-4-1b-2016-05-21

Flake8 changes at:
https://flake8.readthedocs.io/en/latest/changes.html

Flake8-Docstrings changes at:
https://gitlab.com/pycqa/flake8-docstrings/blob/master/HISTORY.rst

HTTMock changes at (raw form):
https://github.com/patrys/httmock/compare/1.2.4...1.2.5

Mock changes at:
https://mock.readthedocs.io/en/latest/changelog.html

Sphinx changes at:
http://www.sphinx-doc.org/en/stable/changes.html

girder/girder_worker,girder/girder_worker,girder/girder_worker