Bump matplotlib from 3.3.4 to 3.4.2

Bumps [matplotlib](https://github.com/matplotlib/matplotlib) from 3.3.4 to 3.4.2.
- [Release notes](https://github.com/matplotlib/matplotlib/releases)
- [Commits](matplotlib/matplotlib@v3.3.4...v3.4.2)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

requirements.txt

@@ -1,7 +1,7 @@
 numpy==1.19.5
 scipy==1.5.4
 scikit-learn
-matplotlib==3.3.4
+matplotlib==3.4.2
 Cython==0.29.22
 imageio==2.9.0
 trimesh==3.9.8