Cloudflare fallback headers and updates eslint and prettier configs

[pbojinov]

Fixes #46

• Adds Cf-Pseudo-IPv4 as a last resort – https://blog.cloudflare.com/eliminating-the-last-reasons-to-not-enable-ipv6/#introducingpseudoipv4
• Updates eslint
• Updates prettier

[Kikobeats]

@pbojinov According to CloudFlare docs, there is another header worth it to be supported:

The three options available for configuring Pseudo IPv4 are:

• Off: This is the default value.
• Add Header: Cloudflare automatically adds the Cf-Pseudo-IPv4 header with a Class E IPv4 address hashed from the original IPv6 address.
• Overwrite Headers - Cloudflare overwrites the existing Cf-Connecting-IP and X-Forwarded-For headers with a pseudo IPv4 address while preserving the real IPv6 address in a Cf-Connecting-IPv6 header.

so if you add support Cf-Connecting-IPv6 as well, that will cover all the possibilities 🙂

[pbojinov]

@Kikobeats thanks for pointing that out. I’ll add that as well.