fix(head.html): Adds robustness to `config.yaml` favicon definitions

Initially assumed that `href` definitions should have `/...` as their
pattern, and `baseURL` would always end with `/`, however the omission
of `/` as the prefix of the former and suffix of the latter
simultaneously, would result in broken favicon paths. Final comment:
`..///...` is not breaking, which is worst case scenario with this fix.