Gorilla websocket with google app engine

Question

I am getting following error when I am running "goapp serve myapp/" from Myproject folder inside src.

go-app-builder: Failed parsing input: parser: bad import "unsafe" in github.com/gorilla/websocket/client.go from GOPATH

my file structure is some something like this

$GOPATH/src
|-github.com/gorilla/websocket
|-MyProject
   |-myapp
      |-app.yaml
      |-mainApp.go (which contain init function and part of app package)

Please let me know how to correct this.

on a related subject, I read that google app provide websocket support only in paid app. Is there a way for me to test my website before getting into payment mode? Or is there a better option that google app engine?