v4.2.0 Catilina support, check for updates, bug fix (daquinoaldo#19)

- Update to mkcert v1.4.0: macOS Catalina compatibility and more. https://github.com/FiloSottile/mkcert/releases/tag/v1.4.0
- Add `REINSTALL=true serve` env variable to force reinstall certs.
- Check for updates if running as compiled executable (downloaded from GitHub releases).
- Update dependencies.
- Add troubleshooting for daquinoaldo#13.

Merge pull request daquinoaldo#13 from daquinoaldo/develop-4.1.0

Develop 4.1.0