Collection of fixes to resolve issues with testing

This implements a number of fixes in order to remedy issues in the testing environment.

Some background: it turns out that the Docker images haven't been updating for the last 3 months. In order to get kombine into the docker image !638 (merged), I went and resolved the cause (it was a linking issue with github and dockerhub). This updated the python 3.7 test image, but the python 2.7 test image has failed. As such. Our python3.7 image has updates such as gwpy 1.0 while the python 2.7 doesn't.

Summary of the changes:

1. Closes #425 (closed): patch to work with emcee3.0
2. Fixes gwutils test failing due to gwpy==1.0
3. Removes the python 2.7 test. My opinion is that since we are so close to python2.7 EOL, rather than spend time fixing the image and getting thing running, let's just cut the chord now. People can still use python2.7, but we won't test on it anymore.