Fix issue with abc.ABCMeta causing dill failures

[kennknowles]

This may be a bug with Dill that needs to be filed upstream.

Imported from Jira BEAM-2685. Original Jira may contain additional context.
Reported by: robertwb.

[ryanthompson591]

.take-issue

I've been working on this with the dill team. I submitted a patch uqfoundation/dill#558, but they have a more complicated patch that fixes this:
uqfoundation/dill#450

Unfortunately their patch did not make it into 0.3.6 of dill.