fix: Extract domains from subdomains (`-md`)

[callightmn]

Hello,

I recently came across the following behavior when trying to discover subdomains of a .net.co domain (let's say example.net.co). Gotator gave me several false positives, including 99.net.co, when given a subdomain in input (let's say api.example.net.co).

This behavior seems to come from isCCSLDDomain which does not filter .net.co domains properly depending on the length of the input (sub)domain:

This is because the check against ccsld (which contains "net.co" in our case) is performed by joining all the values of splitDomain excluding the first one (that's why when given example.net.co it properly filters the domain but not when given api.example.net.co).

A more robust check would be:

[callightmn]

Edit: using https://raw.githubusercontent.com/owasp-amass/amass/master/examples/wordlists/deepmagic.com_top500prefixes.txt

Edit: instead of using a list of ccSLD, you could use a Go library: https://publicsuffix.org/learn/