fix re-export when edition=2018

Author: japaric

src/generate/device.rs

@@ -126,7 +126,7 @@ pub fn render(d: &Device, target: &Target, nightly: bool, device_x: &mut String)
             pub use cortex_m::peripheral::Peripherals as CorePeripherals;
             #[cfg(feature = "rt")]
             pub use cortex_m_rt::interrupt;
-            pub use Interrupt as interrupt;
+            pub use self::Interrupt as interrupt;
         });
 
         if fpu_present {