build(deps): bump torch from 1.6.0 to 1.13.1 in /docs

Bumps [torch](https://github.com/pytorch/pytorch) from 1.6.0 to 1.13.1.
- [Release notes](https://github.com/pytorch/pytorch/releases)
- [Changelog](https://github.com/pytorch/pytorch/blob/main/RELEASE.md)
- [Commits](https://github.com/pytorch/pytorch/compare/v1.6.0...v1.13.1)

---
updated-dependencies:
- dependency-name: torch
  dependency-type: direct:production
...

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

docs/requirements.txt

@@ -1,4 +1,4 @@
-torch==1.6.0
+torch==1.13.1
 matplotlib==3.1.2
 sphinx_rtd_theme==0.5.0
 sphinxcontrib-katex==0.6.1