upgrade mailgun driver

index.js

@@ -1,24 +1,18 @@
 
-var Mailgun = require('mailgun-js');
+const Mailgun = require('mailgun.js');
 
-var SimpleMailgunAdapter = mailgunOptions => {
+const SimpleMailgunAdapter = mailgunOptions => {
   if (!mailgunOptions || !mailgunOptions.apiKey || !mailgunOptions.domain || !mailgunOptions.fromAddress) {
     throw 'SimpleMailgunAdapter requires an API Key, domain, and fromAddress.';
   }
-  var mailgun = Mailgun(mailgunOptions);
-
-  var sendMail = mail => {
-    var data = Object.assign({}, mail, { from: mailgunOptions.fromAddress });
+  const mailgunClient = Mailgun.client({
+    username: 'api',
+    key: mailgunOptions.apiKey
+  });
 
-    return new Promise((resolve, reject) => {
-      mailgun.messages().send(data, (err, body) => {
-        if (typeof err !== 'undefined') {
-          reject(err);
-          return;
-        }
-        resolve(body);
-      });
-    });
+  const sendMail = mail => {
+    const data = Object.assign({}, mail, { from: mailgunOptions.fromAddress });
+    return mailgunClient.messages.create(mailgunOptions.domain, data);
   }
 
   return Object.freeze({