Fix clone macro docs
* Fix clone macro docs
It referenced a "run_fail" attribute, which does not seem to exist.
@@ -136,7 +136,7 @@ use syn::{parse_macro_input, DeriveInput, LitStr};
///
/// Or by using `@default-panic` (if the value fails to get upgraded, it'll panic):
///
-/// ```run_fail
+/// ```should_panic
/// # use glib_macros::clone;
/// # use std::rc::Rc;
/// # let v = Rc::new(1);
