build.rs copy from public to build which should be the other way around

[AlexandreRoba]

Hi, great project! Teach me a lot of think. Thanks. I believe there is an error on the copy function. It copy from public to build and should be the other way around I guess. I can make a pull request if I'm right :p

I replaced the all copy function on build.rs with this:

    Command::new("cp")
        .args(["-a", "./build/.", "./public/"])
        .status()
        .expect("failed to copy folder");