matplotlib/matplotlib: REL: v3.3.1

This is the first bugfix release of the 3.3.x series. This release contains several critical bug-fixes: fix docstring import issues when running Python with optimization fix hist with categorical data, such as with Pandas fix install on BSD systems fix nbagg compatibility with Chrome 84+ fix ordering of scatter marker size in 3D plots fix performance regression when plotting Paths fix reading from URL in imread fix several regressions with new date epoch handling fix some bad constrained and tight layout interactions with colorbars fix use of customized toolbars in TkAgg and WXAgg backends