Change Google reCAPTCHA referrer domain

[cherinyy]

Is your feature request related to a problem? Please describe. In the Chinese mainland, we cannot access www.google.com, so we cannot use Google reCAPTCHA through www.google.com.

Describe the solution you'd like Change Google reCAPTCHA referring domain to www.recaptcha.net.

Describe alternatives you've considered None

Additional context