menpo pins matplotlib<2 on setup.py

Besides the conda package pin, there is another pin at the Python package level, what makes pip installations that depend on menpo go badly.

https://github.com/menpo/menpo/blob/6c2456d2430c6fe8f8fbb6109c249e6c84b26456/setup.py

Example: https://gitlab.idiap.ch/bob/bob.nightlies/builds/44488