feat: support promised request interceptor

[clock157]

1. 支持 Promise 化的 request interceptor

close #28 umijs/umi#2628

[clock157]

没有异议就先合并了，发布 1.1.0

[cathy668]

好像还没支持呢
类型“(url: string, options: RequestOptionsInit) => Promise<{ url: string; options: { headers: { token: string; }; charset?: "utf8" | "gbk" | undefined; requestType?: "json" | "form" | undefined; data?: any; ... 24 more ...; window?: any; }; }>”的参数不能赋给类型“RequestInterceptor”的参数。
类型“Promise<{ url: string; options: { headers: { token: string; }; charset?: "utf8" | "gbk" | undefined; requestType?: "json" | "form" | undefined; data?: any; params?: object | URLSearchParams | undefined; ... 23 more ...; window?: any; }; }>”与类型“{ url?: string | undefined; options?: RequestOptionsInit | undefined; }”不具有相同的属性

[hyzx86]

刚下手 antd , 这不能异步写不下去了啊。。
有其他方案么？