Add regex for punycode domain syntax

You added ".рф" to servers.json (https://github.com/regru/php-whois/commit/dd12d083c818975f05d6253eb900139713c4803f#diff-39cd963adac8f759fde4cfa440663efdR1482) but your regex fails to validate. This should fix (also reported https://github.com/regru/php-whois/issues/22)