Quick checklist

• I am using the latest version of Snowpack and all plugins.

What package manager are you using?

npm

What operating system are you using?

Windows

Describe the bug

<iframe srcdoc="<script src='someFileOnDevServer.js'></script>"></iframe>

results in an error

about:srcdoc:1 Uncaught DOMException: Failed to construct 'WebSocket': The URL 'wss:///' is invalid.
at http://localhost:8080/_snowpack/hmr-client.js:58:16

and because the exception isn't caught, the module fails to load.

Steps to reproduce

1. Load a dev server hsotged file with HMR inside of a srcdoc iframe
2. Error! Uncaught DOMException:

Link to minimal reproducible example (optional)

No response