setup: bump some dev_requirements.txt versions Upgrade notes for these libraries have not been investigated thoroughly, but testing seems to show that it works.

pytest >= 3.3.0, < 4.7
pytest-runner < 5.2
pytest-sugar >= 0.7.0, < 0.10
pytest-benchmark < 3.3
pytest-localserver < 0.6
mock < 3.1
Sphinx < 1.9
WebTest < 2.1