Upgrade mermaid-js to v8.13.2

This fixes a number of issues and introduces some cool new diagrams,
such as Git graph and user journey diagrams:
https://github.com/mermaid-js/mermaid/releases

Changelog: fixed

package.json

@@ -147,7 +147,7 @@
     "lowlight": "^1.20.0",
     "marked": "^0.3.12",
     "mathjax": "3",
-    "mermaid": "^8.11.5",
+    "mermaid": "^8.13.2",
     "minimatch": "^3.0.4",
     "monaco-editor": "^0.25.2",
     "monaco-editor-webpack-plugin": "^4.0.0",