Add an option api_host to custom the reCAPTCHA API server hostname

[moesoha]

The host www.google.com introduced in Google document is blocked in Mainland China. For Chinese users, a solution is to use an official reverse proxy server recaptcha.net. So I add an option api_host(default value: www.google.com) to change the reCAPTCHA API server's hostname.

[excelwebzone]

I can merge it but can you make a few small changes before:

1. Add space between variable and constant:

$apiHost='www.google.com'

to

$apiHost = 'www.google.com'

2. Use sprintf instead of using .:

'https://'.$apiHost.'/recaptcha/api.js';

to

sprintf('https://%s/recaptcha/api.js';', $apiHost)

3. Change new parameters names:

protected $RECAPTCHA_API_SERVER;
protected $RECAPTCHA_API_JS_SERVER;

to

protected $recaptchaApiServer;
protected $recaptchaApiJsServer;

[moesoha]

I followed your advice and committed after fixing code style.

[excelwebzone]

Thanks. I tagged it v1.5.6 👍