Bump plotly from 5.1.0 to 5.2.1

Bumps [plotly](https://github.com/plotly/plotly.py) from 5.1.0 to 5.2.1.
- [Release notes](https://github.com/plotly/plotly.py/releases)
- [Changelog](https://github.com/plotly/plotly.py/blob/master/CHANGELOG.md)
- [Commits](https://github.com/plotly/plotly.py/compare/v5.1.0...v5.2.1)

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

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

requirements-plot.txt

@@ -1,5 +1,5 @@
 # Include all requirements to run the bot.
 -r requirements.txt
 
-plotly==5.1.0
+plotly==5.2.1