Fix SPI_MODE_0 usage in the readme example

Author: martinsp

README.md

@@ -21,14 +21,14 @@ practice.
 extern crate spidev;
 use std::io;
 use std::io::prelude::*;
-use spidev::{Spidev, SpidevOptions, SpidevTransfer, SPI_MODE_0};
+use spidev::{Spidev, SpidevOptions, SpidevTransfer, SpiModeFlags};
 
 fn create_spi() -> io::Result<Spidev> {
     let mut spi = try!(Spidev::open("/dev/spidev0.0"));
     let options = SpidevOptions::new()
          .bits_per_word(8)
          .max_speed_hz(20_000)
-         .mode(SPI_MODE_0)
+         .mode(SpiModeFlags::SPI_MODE_0)
          .build();
     try!(spi.configure(&options));
     Ok(spi)