Make example in readme compatible with 2018 edition

Author: martinsp

README.md

@@ -24,21 +24,21 @@ use std::io::prelude::*;
 use spidev::{Spidev, SpidevOptions, SpidevTransfer, SpiModeFlags};
 
 fn create_spi() -> io::Result<Spidev> {
-    let mut spi = try!(Spidev::open("/dev/spidev0.0"));
+    let mut spi = Spidev::open("/dev/spidev0.0")?;
     let options = SpidevOptions::new()
          .bits_per_word(8)
          .max_speed_hz(20_000)
          .mode(SpiModeFlags::SPI_MODE_0)
          .build();
-    try!(spi.configure(&options));
+    spi.configure(&options)?;
     Ok(spi)
 }
 
 /// perform half duplex operations using Read and Write traits
 fn half_duplex(spi: &mut Spidev) -> io::Result<()> {
     let mut rx_buf = [0_u8; 10];
-    try!(spi.write(&[0x01, 0x02, 0x03]));
-    try!(spi.read(&mut rx_buf));
+    spi.write(&[0x01, 0x02, 0x03])?;
+    spi.read(&mut rx_buf)?;
     println!("{:?}", rx_buf);
     Ok(())
 }
@@ -51,7 +51,7 @@ fn full_duplex(spi: &mut Spidev) -> io::Result<()> {
     let mut rx_buf = [0; 3];
     {
         let mut transfer = SpidevTransfer::read_write(&tx_buf, &mut rx_buf);
-        try!(spi.transfer(&mut transfer));
+        spi.transfer(&mut transfer)?;
     }
     println!("{:?}", rx_buf);
     Ok(())