FIX: browser.js add console.warn (#668)

Close #648

Author: Ari1c

README.md

@@ -223,7 +223,8 @@ for creating client.
     region: 'oss-cn-hangzhou',
     accessKeyId: '<access-key-id>',
     accessKeySecret: '<access-key-secret>',
-    bucket: '<bucket-name>'
+    bucket: '<bucket-name>',
+    stsToken: '<security-token>'
   });
 
   client.list().then((result) => {

lib/browser/client.js

@@ -90,6 +90,10 @@ function Client(options, ctx) {
 module.exports = Client;
 
 Client.initOptions = function initOptions(options) {
+  if (!options.stsToken) {
+    console.warn('Please use STS Token for safety, see more details at https://help.aliyun.com/document_detail/32077.html');
+  }
+
   if (!options
     || !options.accessKeyId
     || !options.accessKeySecret) {