Update mermaid to 11.3.0

Currently, Mermaid 10.9.0 is bundled.

Mermaid 11.3.0 is available with support for [additional node shapes](https://mermaid.js.org/syntax/flowchart.html#expanded-node-shapes-in-mermaid-flowcharts-v11-3-0).

Note: There's a PR https://github.com/asciidoctor/asciidoctor-vscode/pull/888 (Renovate) addressing an update from 10.9.0 to 11.0.0
