Pinned `psutil` dependency on Windows causes unnecessary conflicts

[ankostis]

The psutil Windows-only dependency is pinned to version 5.3.1'. In a python-installation with latest psutilthis will cause it to downgrade from5.4.3` (as of May 2018).
Is there any specific reason for the pinning?

[edit] My quick blame-search did not reveal the reason for the pinning: 02efd88

[pfmoore]

Further note - this causes failures when installing with Python 3.7, as there are no psutil 5.3.1 binaries for Python 3.7 (and I suspect it's unlikely they will be provided, as it's an out of date version).

I created #196 to add Python 3.7 support (remove the pins, add Python 3.7 to CI).

[pfmoore]

Fixed by #196 which has now been merged.