Add Transporter for wasm js target (#42)

* added js target specific roundtrip

* roundtrip_js dial parameter fix

http/transport.go

@@ -25,8 +25,3 @@ type readTrackingBody struct {
 type Transport struct{}
 
 var DefaultTransport RoundTripper = &Transport{}
-
-// roundTrip implements a RoundTripper over HTTP.
-func (t *Transport) RoundTrip(req *Request) (*Response, error) {
-	return roundTrip(req)
-}