fix non-promise example

README.md

@@ -61,12 +61,11 @@ of how to use this library:
 ```javascript
 var le = require('letsencrypt').create({ server: 'staging' });
 
-le.register(
-  { domains: ['example.com'], email: 'user@email.com', agreeTos: true }
-, function (err, results) {
-    console.log(err, results);
-  }
-);
+le.register({ domains: ['example.com'], email: 'user@email.com', agreeTos: true }).then(function (results) {
+  console.log(results);
+}, function (err) {
+  console.error(err);
+});
 ```
 
 You also need some sort of server to handle the acme challenge: