Update promise.md

console.log的输出和展示结果不一致

Author: zihua-1022

docs/promise.md

@@ -79,7 +79,7 @@ let promise = new Promise(function(resolve, reject) {
 });
 
 promise.then(function() {
-  console.log('resolved.');
+  console.log('resolved');
 });
 
 console.log('Hi!');