Changed to add package.json beforehand to make building time shorten

ref: #113

Temporary fix for #112 
@ainoya After confirmation, I found that `cp -nr /tmp/build-screen2/ /tmp/build-screen/` copies whole `build-screen2` into `build-screen`. So after execution of this command, `/tmp/build-screen2/build-screen` was made.
see: https://app.wercker.com/#buildstep/54a0534a6b3ba8733dcc05c7

I don't have any idea to prohibit verbose comands for now.