Graphviz Support

I'm challenged to get this working on my system. That's OK, as I've found efanzh.graphviz-preview (current only supports the DOT layout engine) to be more responsive and offer additional export options.

[PowerShell command prompt]
C:\workspace> cd .\dot-vscode\
C:\workspace\dot-vscode [master ≡ +1 ~3 -0 !]> npm install

> dot-vscode@0.1.0 postinstall C:\workspace\dot-vscode
> node ./node_modules/vscode/bin/install

Detected VS Code engine version: ^1.16.0
Found minimal version that qualifies engine range: 1.16.0
Fetching vscode.d.ts from: https://raw.githubusercontent.com/Microsoft/vscode/787b31c0474e6165390b5a5989c9619e3e16f953/src/vs/vscode.d.ts
vscode.d.ts successfully installed!

audited 137 packages in 3.429s
found 1 low severity vulnerability
  run `npm audit fix` to fix them, or `npm audit` for details
C:\workspace\dot-vscode [master ≡ +1 ~3 -0 !]> npm audit fix
up to date in 0.36s
fixed 0 of 1 vulnerability in 137 scanned packages
  1 vulnerability required manual review and could not be updated
C:\workspace\dot-vscode [master ≡ +1 ~3 -0 !]>

I don't get an advisory telling me which package is at fault, however, I suspect it has to do with graphviz since this isn't working for me. I'll let you know if I find anything.

Reproduce the report with the shown npm install and npm audit commands, then trace the Graphviz support entry point and dependency involved. Done means the responsible package or integration issue is identified and Graphviz support works as intended.