maxwell v1.0.1 Maxwell.Middleware.EncodeJson
Encode request's body to json when request's body is not nil
It will auto add %{'Content-Type': 'application/json'}
to request's headers
Default json_lib is Poison ```ex
Client.ex
use Maxwell.Builder ~(get)a @middleware Maxwell.Middleware.EncodeJson
or
@middleware Maxwell.Middleware.EncodeJson, [contenttype: "application/json", encodefunc: &otherjsonlib.encode/1] ```