fix: easy collections

Author: lucifer

SUMMARY.md

@@ -1,11 +1,7 @@
 ‌
 # Summary​
 
-* 前言
-
-    * [使用指南](introduction.md)
-
-* 高频考题（简单）
+* [高频考题（简单）](./collections/easy.md)
     * [面试题 17.12. BiNode](./problems/binode-lcci.md)
     * [0001.two-sum](https://github.com/azl397985856/leetcode/blob/mast./problems/1.two-sum.md)
     * [0020.Valid Parentheses](./problems/20.valid-parentheses.md)