[Greendns] Replace deprecated resolver.query by resolver.resolve

Usages of `resolver.query` are deprecated[1][2][3] and should
be replaced by `resolver.resolve`.

Fix #818

[1] https://dnspython.readthedocs.io/en/latest/whatsnew.html#id8
[2] https://github.com/rthalley/dnspython/blob/adfc942725bd36d28ec53f7e5480ace9eb543bd8/dns/resolver.py#L1360
[3] https://github.com/rthalley/dnspython/blob/adfc942725bd36d28ec53f7e5480ace9eb543bd8/dns/resolver.py#L1596

eventlet/support/greendns.py

@@ -409,7 +409,7 @@ def end():
         # https://github.com/nameko/nameko/issues/392
         # https://github.com/eventlet/eventlet/issues/363
         if len(qname) == 1:
-            step(self._resolver.query, qname.concatenate(dns.name.root),
+            step(self._resolver.resolve, qname.concatenate(dns.name.root),
                  rdtype, rdclass, tcp, source, raise_on_no_answer=False)
 
         return end()