Update README.md

Author: NJHu

README.md

@@ -1,6 +1,6 @@
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 <p>在武汉打算换工作啦, 有坑位推荐的朋友请加我微信~谢谢~</p>
-<img src="https://raw.githubusercontent.com/NJHu/iOSProject/master/images/wx_code.png" width="28%">
+<img src="https://raw.githubusercontent.com/NJHu/iOSProject/master/images/wx_code.jpg" width="28%">
 </div>