Update msg parsing to not use eval

[vsoch]

This is a quick PR to update message parsing to not use eval. As we discussed in https://github.com/snakemake/snakemake/pull/819#issuecomment-751854197, we want to update snakemake to properly parse a dumped json (from a dict) instead of using repr() and then we can use json.loads() on the server here.

[fgypas]

So, the tests here fail, because we need to use the updated version of snakemake that @vsoch builds in https://github.com/snakemake/snakemake/pull/819

I tested locally the changes from the current pull request in combination with https://github.com/vsoch/snakemake/tree/update/panoptes-logger and the communication between snakemake and panoptes works fine.

[fgypas]

@vsoch With the release of the new snakemake the tests now pass. Can you please add your name to the list of contributors (contributors.md) and then I can merge the branch.

[vsoch]

Added!