isUrl - host_whitelist array option - support array items containing regex/wildcard value

[fogine]

As the title says, it would be cool if I could do:

validator.isUrl(url, {host_whitelist: [
    /^.*slack\.com$/,
]});

This way I could allow dynamic sub-domains in url strings.

Thanks for sharing your work!

[chriso]

Happy to accept a PR 😄