Downloading web extensions with CLI errors

## OS/Web Information

- Web Browser: Chrome
- Local OS: macOS
- Remote OS: macOS
- Remote Architecture: N/A
- `code-server --version`: 4.0.1

## Steps to Reproduce

1. `code-server --install vscodevim.vim`

## Expected

Should install the extension

## Actual

Installs but not as a browser extension

## Logs

## Screenshot


## Notes

@bpmct reported this after talking to someone in the Slack community

This issue can be reproduced in VS Code: Yes/No