update echo-servers

README.md

@@ -238,8 +238,5 @@ cd echo-servers
 ```
 
 **echo-servers/benchmark**<br>
-![echo-servers](html/downloads/echo-servers.jpg)
-
-Note: The client and servers are located in the same computer, the results are random, for reference only.
-In general, the performance of these libraries are similar, each has its own advantages.
+![echo-servers](html/downloads/echo-servers.png)
 

readme_cn.md

@@ -237,7 +237,7 @@ cd echo-servers
 ```
 
 **echo-servers/benchmark**<br>
-![echo-servers](html/downloads/echo-servers.jpg)
+![echo-servers](html/downloads/echo-servers.png)
 
 注：因为客户端和服务端测试位于同一台机器，上图结果仅供参考。总的来说，这些库性能接近，各有千秋。