Repro steps:

1. Add mailto link in README.md, e.g. [Email me!](mailto:me@website.com?Subject=Repro).
2. Run "vsce package"
3. I get the following error:
   Error: Couldn't detect the repository where this extension is published. The link 'mailto:me@website.com?Subject=Repro' will be broken in README.md. Please provide the repository URL in package.json or use the --baseContentUrl and --baseImagesUrl options.

If I run "vsce package --baseContentUrl" it ends up adding "true/" to the link like so:
[Email me!](true/mailto:me@website.com?Subject=Repro)

I would expect vsce to ignore mailto links such that they actually work when the package is installed and the user views the readme.