Modify more fast

[Kei Kamikawa]

I want to change from "net/http" to "valyala/fasthttp" used in requests.go

https://github.com/valyala/fasthttp#http-client-comparison-with-nethttp

I wonder if use "valyala/fasthttp" then will be really faster than "net/http"...

However it is also fun to try various:+1:

[Kei Kamikawa]

Not need it in this era