fix: use eprintln to print errors

src/main.rs

@@ -29,7 +29,7 @@ fn main() -> Result<()> {
                     break;
                 }
                 Err(ShellError::NotFound(cmd)) => {
-                    println!("{}: command not found", cmd.get_program().to_string_lossy())
+                    eprintln!("{}: command not found", cmd.get_program().to_string_lossy())
                 }
                 Err(ShellError::ExecuteFailure(msg)) => {
                     eprintln!("{}", msg)
@@ -39,7 +39,7 @@ fn main() -> Result<()> {
                 break;
             }
             Err(err) => {
-                println!("Error: {:?}", err);
+                eprintln!("Error: {:?}", err);
                 break;
             }
         }