ggplot broken

[staeff]

ggplot as currently installed with the Docker file due to a bug, that is fixed with yhat/ggpy#668 but does not get merged and released by yhat.

To reproduce the problem fill a cell of a notebook with the command from ggplot import * and run it.

The pull request commiter made a release under his github account https://github.com/hbasria/ggpy.

#822 fixes the issue by installing the pull request commiters release and adds a test for it the library to work.