Clean up error display

src/main.rs

@@ -33,7 +33,7 @@ fn run_prompt() -> anyhow::Result<()> {
         let line = line_res.with_context(|| "failed to read input line")?;
         let run_res = jlox_rust::run(&line);
         if let Err(err) = run_res {
-            eprintln!("{err:?}");
+            eprintln!("{err}");
         }
 
         print_prompt()?;