Fix the signer signing an invalid certificate

[riijj]

The Signer will sign an invalid certificate when hostname is an IPV6 address

E.g :
Assuming the URL is https://[2606:4700:4700::1111]:443 , the CommonName of signed certificate will be: [2606 , the certificate is invalid.

this PR will fix the bug.

[elazarl]

Sounds good, isn't there something in the stdlib to do that?

[riijj]

Sounds good, isn't there something in the stdlib to do that?

Forgive me , I'm not sure what you mean

[elazarl]

@riijj a function to parse URL and take IPv6 into account