Fix no_std build.

src/error.rs

@@ -2,7 +2,7 @@
 
 use crate::token::Position;
 
-use crate::stdlib::{char, error::Error, fmt, string::String};
+use crate::stdlib::{boxed::Box, char, error::Error, fmt, string::String};
 
 /// Error when tokenizing the script text.
 #[derive(Debug, Eq, PartialEq, Hash, Clone)]