Log Message:
py-matplotlib: update to 2.1.0

v2.1.0:

This is the second minor release in the Matplotlib 2.x series and the first
release with major new features since 1.5.

This release contains approximately 2 years worth of work by 275 contributors
across over 950 pull requests. Highlights from this release include:

* support for string categorical values
* export of animations to interactive javascript widgets
* major overhaul of polar plots
* reproducible output for ps/eps, pdf, and svg backends
* performance improvements in drawing lines and images
* GUIs show a busy cursor while rendering the plot
* along with many other enhancements and bug fixes.