Warning about clock plot and fixed formatters.

[jceirving]

In the underlying plotting code, seismosocialdistancing.py, there is now a matplotlib warning raised when plotting the clock plots. Matplotlib version is "matplotlib-base 3.3.3", and Pandas is 1.1.4, both from conda-forge. This isn't a problem for the code itself, it's the imported packages, and has been raised as an issue there for a few months. However, it would prove un-nerving to users unfamiliar to these warnings, and can be alleviated.

The warning is "UserWarning: FixedFormatter should only be used together with FixedLocator". THe error can be alleviated by a dummy call - I added the following after line 605: ax.set_yticks(ax.get_yticks())