matplotlib 3.0.0 bug affecting plots

[andrewheusser]

@jeremymanning - There is a bug in the latest release of matplotlib (3.0.0) that causes some plots to get compressed along a single axis (matplotlib/matplotlib#12239). I found that this affected hypertools when I upgraded matplotlib. There is an issue for it and it looks like people are currently working on a fix. I was able to get around it by reverting back to matplotlib 2.2.3. Until it is fixed, we could require matplotlib<3.0.0

[jeremymanning]

@andrewheusser that's an annoying bug! Good catch. And I agree with your proposed fixed-- let's require matplotlib>=1.5.1,<3.0.0. Do you want to do the honors and then push a minor 0.5.2 release?