bokeh required for tests to pass

[taylorgibson]

I just went through the instructions in DEVELOPERS.md and when running make test 115 tests failed because bokeh was not installed in the environment.

Installing bokeh allows all 346 tests to pass (2 warnings).

bokeh should be added to the osx_environment.yml and linux_environment.yml if it is required for the tests to pass.

[adnanhemani]

Hi, placing comments onto your PR.

[davidwagner]

Thank you for reporting this! Based on the discussion in #580, my sense is that the best short-term solution might be to update DEVELOPERS.md to mention the dependence on requirements-tests.txt. Moving to tox sounds like a longer-term project. But I don't have strong opinions and I expect I'll be glad to go with whatever you and Adnan come up with.