修正ch15-01-box的代码

src/ch15-01-box.md

@@ -71,7 +71,7 @@ enum List {
 <span class="filename">文件名: src/main.rs</span>
 
 ```rust,ignore
-use List::{Cons, Nil};
+use crate::List::{Cons, Nil};
 
 fn main() {
     let list = Cons(1, Cons(2, Cons(3, Nil)));
@@ -145,7 +145,7 @@ enum List {
     Nil,
 }
 
-use List::{Cons, Nil};
+use crate::List::{Cons, Nil};
 
 fn main() {
     let list = Cons(1,