Fails to compile on Windows

[fenhl]

The crate-level docs say this crate is cross-platform, but on Windows the compilation fails with this error:

    Checking futures v0.1.31
    Checking chase v0.1.8 (C:\Users\fenhl\git\github.com\fenhl\chase-rs\stage)
error: could not compile `chase`

To learn more, run the command again with --verbose.
error[E0425]: cannot find function `get_file_id` in this scope
  --> src\sync.rs:72:35
   |
72 |                     let file_id = get_file_id(&file)?;
   |                                   ^^^^^^^^^^^ not found in this scope

The reason is that get_file_id is only defined on #[cfg(unix)].