Docker does not access current gmxpy version

[eirrgang]

A shell command had unexpected behavior and the Docker build uses an old version of the gmxapi source.

The /home/jovyan/gmxpy directory should not have existed in the gromacs-gmxapi image.

[eirrgang]

This might have been a transient issue from a bad parent image. The current devel branch of gromacs-gmxapi doesn't seem to leave the offending directory in place.