修正ch15中的代码

src/ch15-04-rc.md

@@ -34,7 +34,7 @@ enum List {
     Nil,
 }
 
-use List::{Cons, Nil};
+use crate::List::{Cons, Nil};
 
 fn main() {
     let a = Cons(5,
@@ -76,7 +76,7 @@ enum List {
     Nil,
 }
 
-use List::{Cons, Nil};
+use crate::List::{Cons, Nil};
 use std::rc::Rc;
 
 fn main() {
@@ -106,7 +106,7 @@ fn main() {
 #     Nil,
 # }
 #
-# use List::{Cons, Nil};
+# use crate::List::{Cons, Nil};
 # use std::rc::Rc;
 #
 fn main() {

src/ch15-05-interior-mutability.md

@@ -272,7 +272,7 @@ enum List {
     Nil,
 }
 
-use List::{Cons, Nil};
+use crate::List::{Cons, Nil};
 use std::rc::Rc;
 use std::cell::RefCell;
 

src/ch15-06-reference-cycles.md

@@ -19,7 +19,7 @@ doc tests do; the `use List` fails if this listing is put within a main -->
 # fn main() {}
 use std::rc::Rc;
 use std::cell::RefCell;
-use List::{Cons, Nil};
+use crate::List::{Cons, Nil};
 
 #[derive(Debug)]
 enum List {
@@ -46,7 +46,7 @@ impl List {
 <span class="filename">Filename: src/main.rs</span>
 
 ```rust
-# use List::{Cons, Nil};
+# use crate::List::{Cons, Nil};
 # use std::rc::Rc;
 # use std::cell::RefCell;
 # #[derive(Debug)]