Log Message:
py-matplotlib: updated to 3.1.3

REL: v3.1.3
This is the final planned release of the 3.1.x series.

This release contains several critical bug-fixes:
- suppress a warning with Pandas 1.0
- support pillow >= 7
- support dateutils >= 2.8.1
- prevent an infinite recursion
- do not clobber non-python registered signal handler
- fix path intersection computation with 0 length segments
- fix performance regression in draw_idle
- several minor bugs