Update create_file to use std::io::FilePermission

    $ rustc -v
    rustc 0.11-pre-nightly (e454851 2014-05-08 06:11:37 -0700)
    $ make
    ...
    error: src/create_file.rs
     * Build Compilation Output
      src/create_file.rs:29:48: 29:62 error: mismatched types: expected `std::io::FilePermission` but found `u32` (expected struct std::io::FilePermission but found u32)
      src/create_file.rs:29     let result = fs::mkdir(&Path::new("docs"), S_IRWXU as u32);
                                                                           ^~~~~~~~~~~~~~
      error: aborting due to previous error
    ...