Remove unnecessary to_string

src/main.rs

@@ -73,7 +73,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     let matches = match opts.parse(&args[1..]) {
         Ok(m) => m,
         Err(f) => {
-            println!("{}", f.to_string());
+            println!("{}", f);
             println!("{}", opts.usage(&program));
             std::process::exit(1);
         }