Matplotlib version conflict

[kescobo]

Tried to install poretools in a fresh environment:

error: Setup script exited with
Beginning with Matplotlib 3.1, Python 3.6 or above is required.

This may be due to an out of date pip.

Make sure you have pip >= 9.0.1.

$ pip --version
pip 19.1 from /usr/local/lib/python2.7/site-packages/pip (python 2.7)

I was able to pip install matplotlib manually, and then installation worked fine.