test: Change the expected error message on iface-test.rs to contain "trait" instead of "interface"

Author: pcwalton

src/test/compile-fail/iface-test.rs

@@ -1,5 +1,5 @@
 iface foo { fn foo(); }
 
-impl of int for uint { fn foo() {} } //~ ERROR interface
+impl of int for uint { fn foo() {} } //~ ERROR trait
 
 fn main() {}