remove superfluous mut

src/bin/main.rs

@@ -42,7 +42,7 @@ fn main() {
         let _ = rl.load_history(&hist);
     }
 
-    let mut vt = Rc::new(RefCell::new(VTable::new()));
+    let vt = Rc::new(RefCell::new(VTable::new()));
     // if we fail to get stdlib we can just use this one
     let mut ft = Rc::new(RefCell::new(FTable::new()));
     match get_stdlib() {