Update docs/chapter_searching/hashing_search.md

Co-authored-by: Justin Tse <xiefahit@gmail.com>

docs/chapter_searching/hashing_search.md

@@ -173,10 +173,10 @@ comments: true
 
     ```typescript title="hashing_search.ts"
     /* 哈希查找（链表） */
-    function hashingSearch1(map: Map<number, any>, target: number) {
+    function hashingSearch1(map: Map<number, ListNode>, target: number): ListNode | null {
         // 哈希表的 key: 目标结点值，value: 结点对象
         // 若哈希表中无此 key ，返回 null
-        return map.has(target) ? map.get(target) : null;
+        return map.has(target) ? map.get(target) as ListNode : null;
     }
     ```