Fix pattern for co.ac

Author: malkusch

src/Phois/Whois/whois.servers.json

@@ -569,7 +569,7 @@
     ],
     "co.ac": [
         "whois.nic.ac",
-        "Available"
+        "not registered"
     ],
     "co.at": [
         "whois.nic.at",