Update README.md

README.md

@@ -20,7 +20,7 @@
 
 <p align="left">
 <a href="https://e.coding.net/?utm_source=macrozheng&utm_medium=banner&utm_campaign=march2019" target="_blank">
-  <img src="http://macro-oss.oss-cn-shenzhen.aliyuncs.com/mall/banner/coding.jpg" width=""/>
+  <img src="http://macro-oss.oss-cn-shenzhen.aliyuncs.com/mall/banner/coding.png" width=""/>
  </a>
 </p>