[Dependabot]: Update sphinxcontrib-mermaid requirement

Updates the requirements on [sphinxcontrib-mermaid](https://github.com/mgaitan/sphinxcontrib-mermaid) to permit the latest version.
- [Changelog](https://github.com/mgaitan/sphinxcontrib-mermaid/blob/master/CHANGELOG.md)
- [Commits](mgaitan/sphinxcontrib-mermaid@1.2.0...2.0.0)

---
updated-dependencies:
- dependency-name: sphinxcontrib-mermaid
  dependency-version: 2.0.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

doc/requirements.txt

@@ -9,7 +9,7 @@ docutils_stubs ~= 0.0.22
 sphinx_rtd_theme ~= 3.0
 
 # Sphinx Extenstions
-sphinxcontrib-mermaid ~= 1.2
+sphinxcontrib-mermaid ~= 2.0
 autoapi ~= 2.0.1
 sphinx_design ~= 0.6
 sphinx-copybutton ~= 0.5