Fix docker build

I think I've tracked down the failures of pymc3 to a switch to theano-pymc (see https://github.com/pymc-devs/pymc/releases/tag/v3.10.0). Hopefully, this change will be sufficient to fix our install.

I'm going to do a little more tinkering and testing, but hopefully, we can get this in soon.

Update: It looks like things are working well now. I pushed updated containers while I was working on it so that the rest of the tests will work.