don't promisify node's dns; fix https://github.com/Daplie/node-greenlock/issues/69

lib/utils.js

@@ -4,8 +4,7 @@ var path = require('path');
 var homeRe = new RegExp("^~(\\/|\\\\|\\" + path.sep + ")");
 var re = /^[a-zA-Z0-9\.\-]+$/;
 var punycode = require('punycode');
-var PromiseA = require('bluebird');
-var dns = PromiseA.promisifyAll(require('dns'));
+var dnsResolveMxAsync = require('util').promisify(require('dns').resolveMx);
 
 module.exports.attachCertInfo = function (results) {
   // XXX Note: Parsing the certificate info comes at a great cost (~500kb)
@@ -107,10 +106,10 @@ module.exports.testEmail = function (email) {
   if (2 !== parts.length || !parts[0] || !parts[1]) {
     err = new Error("malformed email address '" + email + "'");
     err.code = 'E_EMAIL';
-    return PromiseA.reject(err);
+    return Promise.reject(err);
   }
 
-  return dns.resolveMxAsync(parts[1]).then(function (records) {
+  return dnsResolveMxAsync(parts[1]).then(function (records) {
     // records only returns when there is data
     if (!records.length) {
       throw new Error("sanity check fail: success, but no MX records returned");
@@ -120,7 +119,7 @@ module.exports.testEmail = function (email) {
     if ('ENODATA' === err.code) {
       err = new Error("no MX records found for '" + parts[1] + "'");
       err.code = 'E_EMAIL';
-      return PromiseA.reject(err);
+      return Promise.reject(err);
     }
   });
 };