Adds XPath tester to XPATH.md

Author: cyrilbois

XPATH.md

@@ -7,6 +7,7 @@
 - [XPath tutorial](http://www.zvon.org/xxl/XPathTutorial/)
 - [阮一峰的XPath学习笔记](http://www.ruanyifeng.com/blog/2009/07/xpath_path_expressions.html)
 - [测试XPath的网站](https://www.freeformatter.com/xpath-tester.html)
+- [XPath tester](https://extendsclass.com/xpath-tester.html)
 
 代码并没有完全测试完，可能还有bug，欢迎跟我反馈。
 
@@ -354,4 +355,4 @@ els = set(es1) & set(es2)
 - [XPath的一些高级用法-简书](https://www.jianshu.com/p/4fef4142b33f)
 - [XPath Quicksheet](https://devhints.io/xpath)
 
-如有其他资料，欢迎提[Issues](https://github.com/openatx/uiautomator2/issues/new)补充
+如有其他资料，欢迎提[Issues](https://github.com/openatx/uiautomator2/issues/new)补充