Make Extract::suffixExists protected

[Gman98ish]

Currently the suffixExists method on the Extract class is private, it would be useful if it was protected, so you could override default behavior and provide an alternate data source

[Rohaq]

This would be useful; we've got a use case where we need to validate the TLD, but also have a limited list of additional extensions we want to allow for some local domains without just allowing for any TLD.

[layershifter]

Release in 1.2.7 ✌️