Fix pandas/numpy dependency issues for Docker

[truth-quark]

There's some weird dependency problems which appear to arise out of newer Docker container builds. While building a new container on a new Ubuntu install, the setup tried installing pandas-1.4.0, this broke due to some conflict with numpy 1.17.x. The install "completed" with errors, but pytest failed to get started with 30+ AttributeError: module 'numpy.random' has no attribute 'BitGenerator' errors.

• Mitch thinks we should not be held to numpy <1.18, so suspects we've got a bad dependency somewhere
• Pegging pandas back to 1.3.3 in requirements.txt solved the dependencies bug temporarily
• Possibly related to GDAL dependencies?

[truth-quark]

This might be solved now from the minor fixes #346 work.

[mwheeler]

I think so... not in an ideal way, but it is fixed - we require a newer numpy version that has BitGenerator now even though we don't use it (to satisfy the thirdparty library that does need it but didn't get it due to PIP / Ubuntu apt weirdness)