Fix dns.resolve() with 'PTR' throws Error: Unknown type "PTR"

Fixes #1038

lib/dns.js

@@ -247,7 +247,7 @@ var resolveMap = { A: exports.resolve4,
                    MX: exports.resolveMx,
                    TXT: exports.resolveTxt,
                    SRV: exports.resolveSrv,
-                   PTR: exports.resolvePtr,
+                   PTR: exports.reverse,
                    NS: exports.resolveNs,
                    CNAME: exports.resolveCname };
 

test/simple/test-c-ares.js

@@ -58,3 +58,9 @@ dns.lookup('ipv6.google.com', function(error, result, addressType) {
   //assert.equal('string', typeof result);
   assert.equal(6, addressType);
 });
+
+dns.resolve('127.0.0.1', 'PTR', function(error, domains) {
+  if (error) throw error;
+  assert.ok(Array.isArray(domains));
+});
+