FIX #220 skip unix permission check on windows when loading webp binaries

[SightStudio]

skip chmod command on windows when load cwebp, dwebp binaries.

WebpHandler in scrimage-webp

private static boolean setExecutable(Path output) throws IOException {
    try {
        return new ProcessBuilder("chmod", "+x", output.toAbsolutePath().toString())
            .start()
            .waitFor(30, TimeUnit.SECONDS);
    } catch (InterruptedException e) {
        throw new IOException(e);
    }
}

[sksamuel]

Nice, thanks. Will release a version with this fix.