Bump pypandoc from 1.12 to 1.13 (#592)

Bumps [pypandoc](https://github.com/JessicaTegner/pypandoc) from 1.12 to 1.13.
- [Release notes](https://github.com/JessicaTegner/pypandoc/releases)
- [Changelog](https://github.com/JessicaTegner/pypandoc/blob/master/release.md)
- [Commits](JessicaTegner/pypandoc@v1.12...v1.13)

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

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

Author: dependabot[bot]

requirements/requirements_docs.txt

@@ -1,4 +1,4 @@
-pypandoc==1.12
+pypandoc==1.13
 imageio==2.34.0
 numpydoc==1.6.0
 imageio-ffmpeg==0.4.7