Update README.md

Author: caison

README.md

@@ -101,7 +101,7 @@ TCP状态变迁图、TCP相关常见问题概念(三次握手，四次挥手)，
 
 
 <div align="center">
-    <img src="https://user-gold-cdn.xitu.io/2019/9/28/16d758d532790461?w=471&h=248&f=png&s=29216" >
+    <img src="https://camo.githubusercontent.com/f389c9459f1460ef11a7dca6f40a6cdea5182a8b/68747470733a2f2f757365722d676f6c642d63646e2e786974752e696f2f323031392f392f32382f313664373538643533323739303436313f773d34373126683d32343826663d706e6726733d3239323136" >
 </div>