实现目标：
/*
* axios
* http://www.axios-js.com/zh-cn/docs/
*
* 封装的配置项
* url
* method
* baseURL
* transformRequest
* headers
* params
* data
* withCredentials
* ...
* axios.interceptors
* .request.use()
* .request.eject()
* .response.use()
* .response.eject()
*/