Support the "Registrar WHOIS Server" key name for the referral

The ICANN “Registry Registration Data Directory Services
Consistent Labeling and Display Policy” [1] renames the key
from "WHOIS Server" to this.

Remove duplicate "whois server" entry, as noticed by @devl00p

Fixes joepie91#131

[1] https://www.icann.org/resources/pages/rdds-labeling-policy-2017-02-01-en

Author: Ángel González

pythonwhois/net.py

@@ -61,7 +61,7 @@ def get_whois_raw(domain, server="", previous=None, rfc3490=True, never_cut=Fals
 		new_list = [response] + previous
 	server_list.append(target_server)
 	for line in [x.strip() for x in response.splitlines()]:
-		match = re.match("(refer|whois server|referral url|whois server|registrar whois):\s*([^\s]+\.[^\s]+)", line, re.IGNORECASE)
+		match = re.match("(refer|whois server|referral url|registrar whois(?: server)?):\s*([^\s]+\.[^\s]+)", line, re.IGNORECASE)
 		if match is not None:
 			referal_server = match.group(2)
 			if referal_server != server and "://" not in referal_server: # We want to ignore anything non-WHOIS (eg. HTTP) for now.

pythonwhois/parse.py

@@ -140,7 +140,8 @@ def precompile_regexes(source, flags=0):
 					 'Domain Registrar :\s?(?P<val>.+)',
 					 'Registration Service Provider: (?P<val>.+)',
 					 '\tName:\t\s(?P<val>.+)'],
-		'whois_server':		['Whois Server:\s?(?P<val>.+)',
+		'whois_server':		['Registrar WHOIS Server:\s?(?P<val>.+)',
+					 'Whois Server:\s?(?P<val>.+)',
 					 'Registrar Whois:\s?(?P<val>.+)'],
 		'nameservers':		['Name Server:[ ]*(?P<val>[^ ]+)',
 					 'Nameservers:[ ]*(?P<val>[^ ]+)',