Update webpack-dev-middleware

[p2edwards]

Description

Update webpack-dev-middleware to a newer version.

Notes

The path traversal vulnerability patched by this update does not seem to affect us directly:

• We don't use the writeToDisk option mentioned in the CVE
• We don't expose webpack-dev-server to public traffic nor use it in production

That said, it's good to update anyway. Someone self-hosting or developing might be running things a little differently.

[p2edwards]

Closed by #4992 (upgrades webpack-dev-middleware to ^6.1.3, which includes the patch from 6.1.2)