Bump matplotlib from 3.4.3 to 3.5.1

Bumps [matplotlib](https://github.com/matplotlib/matplotlib) from 3.4.3 to 3.5.1.
- [Release notes](https://github.com/matplotlib/matplotlib/releases)
- [Commits](https://github.com/matplotlib/matplotlib/compare/v3.4.3...v3.5.1)

---
updated-dependencies:
- dependency-name: matplotlib
dependency-type: direct:production
update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -1,6 +1,6 @@
 aiortc==1.2.1
 av==8.0.3
-matplotlib==3.4.3
+matplotlib==3.5.1
 numpy==1.21.4
 opencv-python-headless==4.5.4.60
 pydub==0.25.1