docs: Update sponsor banner (#268)

Author: jdneo

README.md

@@ -21,7 +21,7 @@
 </p>
 
 ## Sponsor
-[![coding](https://raw.githubusercontent.com/jdneo/vscode-leetcode/master/docs/imgs/sponsor_coding.jpg)](https://e.coding.net/?utm_source=leetcode)
+[![coding](https://raw.githubusercontent.com/jdneo/vscode-leetcode/master/docs/imgs/sponsor_coding.png)](https://e.coding.net/?utm_source=leetcode)
 
 - [English Document](#Requirements)
 - [中文文档](https://github.com/jdneo/vscode-leetcode/blob/master/docs/README_zh-CN.md)

docs/README_zh-CN.md

@@ -21,7 +21,7 @@
 </p>
 
 ## 赞助
-[![coding](https://raw.githubusercontent.com/jdneo/vscode-leetcode/master/docs/imgs/sponsor_coding.jpg)](https://e.coding.net/?utm_source=leetcode)
+[![coding](https://raw.githubusercontent.com/jdneo/vscode-leetcode/master/docs/imgs/sponsor_coding.png)](https://e.coding.net/?utm_source=leetcode)
 
 - [English Document](#Requirements)
 - [中文文档](https://github.com/jdneo/vscode-leetcode/blob/master/docs/README_zh-CN.md)