Upgrade Mermaid to 8.0.0

We were using 8.0.0-rc.8 previously, and there appears to be significant
new dependencies.

package.json

@@ -90,7 +90,7 @@
     "jszip-utils": "^0.0.2",
     "katex": "^0.10.0",
     "marked": "^0.3.12",
-    "mermaid": "^8.0.0-rc.8",
+    "mermaid": "^8.0.0",
     "monaco-editor": "^0.15.6",
     "monaco-editor-webpack-plugin": "^1.7.0",
     "mousetrap": "^1.4.6",