matplotlib/matplotlib: REL: v3.3.3

This is the third bugfix release of the 3.3.x series. This release contains several critical bug-fixes: Fix calls to Axis.grid with argument visible=True. Fix fully masked imshow. Fix inconsistent color mapping in scatter for 3D plots. Fix notebook/nbAgg figures when used with ipywidgets in the same cell. Fix notebook/nbAgg/WebAgg on older (e.g., Firefox ESR) browsers. Fix pcolormesh with datetime coordinates. Fix performance regression with datetimes. Fix singular ticks with small log ranges. Fix timers/animations on wx and notebook backends. Remove certifi as a hard runtime dependency.