tidy: Use `Fail::iter_causes` instead of `e.causes().skip(1)`

The `iter_causes` method does the `skip(1)` for us and `e.causes()` is now
deprecated. Unfortunately, `Fail::iter_causes` is only implemented on the
trait *object*, not a provided method for all implementations of the trait. This
means that calling it is slightly less ergonomic...

src/main.rs

@@ -13,7 +13,7 @@ fn main() {
     setup_panic!();
     if let Err(e) = run() {
         eprintln!("{}", e);
-        for cause in e.causes().skip(1) {
+        for cause in Fail::iter_causes(&e) {
             eprintln!("Caused by: {}", cause);
         }
         ::std::process::exit(1);