Update matplotlib requirement from ~=3.3.1 to ~=3.3.2 (#634)

Updates the requirements on [matplotlib](https://github.com/matplotlib/matplotlib) to permit the latest version.
- [Release notes](https://github.com/matplotlib/matplotlib/releases)
- [Commits](matplotlib/matplotlib@v3.3.1...v3.3.2)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements-dev.txt

@@ -5,7 +5,7 @@ pytest ~=6.1.0
 vcrpy ~=4.1.0
 doctr ~=1.8.0
 ipython ~=7.18.1
-matplotlib ~=3.3.1
+matplotlib ~=3.3.2
 numpydoc ~=1.1.0
 requests-mock ~=1.8.0
 sphinx ~=3.2.1