Fix sphinxcontrib-mermaid extension import path

Author: jan-janssen

docs/_config.yml

@@ -15,7 +15,7 @@ launch_buttons:
 
 sphinx:
   extra_extensions:
-  - 'sphinxcontrib-mermaid'
+  - 'sphinxcontrib.mermaid'
   - 'sphinx.ext.autodoc'
   - 'sphinx.ext.napoleon'
   - 'sphinx.ext.viewcode'