Fix test

Author: Manishearth

src/test/run-pass/epoch-gate-feature.rs

@@ -11,7 +11,7 @@
 // Checks if the correct registers are being used to pass arguments
 // when the sysv64 ABI is specified.
 
-// compile-flags: -Zedition=2018
+#![feature(rust_2018_preview)]
 
 pub trait Foo {}