update example config format

Author: jemygraw

demo/config.js.example

@@ -1,8 +1,8 @@
 module.exports = {
-    'ACCESS_KEY': '<Your Access Key>',  // https://portal.qiniu.com/user/key
-    'SECRET_KEY': '<Your Secret Key>',
-    'Bucket_Name': '<Your Bucket Name>',
+    'AccessKey': '<Your Access Key>',  // https://portal.qiniu.com/user/key
+    'SecretKey': '<Your Secret Key>',
+    'Bucket': '<Your Bucket Name>',
     'Port': 19110,
-    'Uptoken_Url': 'uptoken',
+    'UptokenUrl': 'uptoken',
     'Domain': '<Your Bucket Name>' // bucket domain eg:http://qiniu-plupload.qiniudn.com/
 };