algorithm<recursion>: add sumN

Author: careteenL

src/algorithm/recursion/sumN.md

@@ -15,8 +15,9 @@
 
 ## 实现
 
-[递归详细实现及测试用例](./sumN.js#L10)
-[位运算详细实现及测试用例](./sumN.js#L31)
+- [递归详细实现](./sumN.js#L10)
+- [位运算详细实现](./sumN.js#L31)
+- [测试用例](../../../test/recursion.spec.js)
 
 ## 总结