Update to Mermaid to v 8.4.0

[ericwastaken]

PR Summary

This PR:

• Updates the mermaid dependency in the index.html file to Mermaid v 8.4.0 to introduce support for the latest features.
• Fixes a few typos in Code.gs.
• Packages an updated version of /dist/index.html.

The Release notes for Mermaid 8.4.0 are: https://github.com/knsv/mermaid/releases/tag/8.4.0

Testing

After making this change, this was tested locally and on a google doc.

Test Steps:

• npm run build
• Open a Google Doc then select Tools, Script Editor to open the Google Apps Script editor. Name the project anything useful. (Example: Mermaid Fork Test). This name will show in the Add-Ons menu for the google doc.
• Add a new html file to the project called index.html and deploy the contents of /dist/index.html.
• Replace the entire contents of Code.gs in the project with the contents in /google scripts/Code.gs.
• Back on the doc, using the add-on menu, test adding a diagram, then editing, etc.

[renanlecaro]

Gosh, sorry, i somehow didn't get any notifications for the activity on this repo, i'll have a look at your code