fix bug

安卓平台不能设置推送标题,原因是json结构错了

http://docs.jpush.cn/display/dev/Push-API-v3#Push-API-v3-android

before:

```
  "notification": {
    "platform": "android",
    "alert": "alert",
    "title": "title"
  }
```

after:

```
  "notification": {
    "android": {
      "alert": "alert",
      "title": "title"
    }
  }
```