Bump dash from 1.9.1 to 2.15.0 in /docs

Bumps [dash](https://github.com/plotly/dash) from 1.9.1 to 2.15.0.
- [Release notes](https://github.com/plotly/dash/releases)
- [Changelog](https://github.com/plotly/dash/blob/dev/CHANGELOG.md)
- [Commits](plotly/dash@v1.9.1...v2.15.0)

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

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

docs/requirements.txt

@@ -2,7 +2,7 @@ plotly==4.5.4
 numpy==1.22.0
 pandas==1.0.3
 shap==0.32.1
-dash==1.9.1
+dash==2.15.0
 dash-bootstrap-components==0.9.1
 dash-core-components==1.8.1
 dash-daq==0.5.0