Replace deprecated tempdir dependency with tempfile (#11588)

`Tempdir` is deprecated, but the functionality has been merged into
another crate: `tempfile`. This commit removes all `tempdir` dependencies
and replaces them with `tempfile` and the equivalent bindings.

Fixes #11560

ethcore/engines/basic-authority/src/lib.rs

@@ -230,12 +230,12 @@ mod tests {
 		header::Header,
 		engines::{Seal, SealingState}
 	};
-	use tempdir::TempDir;
+	use tempfile::TempDir;
 
 	/// Create a new test chain spec with `BasicAuthority` consensus engine.
 	fn new_test_authority() -> Spec {
 		let bytes: &[u8] = include_bytes!("../res/basic_authority.json");
-		let tempdir = TempDir::new("").unwrap();
+		let tempdir = TempDir::new().unwrap();
 		Spec::load(&tempdir.path(), bytes).expect("invalid chain spec")
 	}