Dependancy missing

[dyve]

Python 2.7, Django 1.11 and django-health-check 3.3.0 crash on a missing dependency:

File "/Users/dylan/.pyenv/versions/meetnetten/lib/python2.7/site-packages/health_check/views.py", line 2, in <module>
    from concurrent.futures import ThreadPoolExecutor
ImportError: No module named concurrent.futures

Reverting to 2.4.0 resolves this error for now.

[dyve]

Tox only runs Python 3, which does not have this issue.

I'd suggest following Django support policy, and support Python 2.7 + Django 1.11 during LTS period.

I can do a PR with an altered tox setup. Easiest solution for Python 2.7 would be to document that futures needs to be added to requirements.txt manually?

[dyve]

Upon cloning the repo I discovered the ChangeLog (somehow not visible on GitHub for me, will investigate). Dropping Python 2 is clearly documented, so this issue can be closed.