Update screenshots. Use png instead of jpgs. (#5770)

README.md

@@ -138,7 +138,7 @@ firewall-cmd --reload
 ## Test using Minio Browser
 Minio Server comes with an embedded web based object browser. Point your web browser to http://127.0.0.1:9000 ensure your server has started successfully.
 
-![Screenshot](https://github.com/minio/minio/blob/master/docs/screenshots/minio-browser.jpg?raw=true)
+![Screenshot](https://github.com/minio/minio/blob/master/docs/screenshots/minio-browser.png?raw=true)
 
 ## Test using Minio Client `mc`
 `mc` provides a modern alternative to UNIX commands like ls, cat, cp, mirror, diff etc. It supports filesystems and Amazon S3 compatible cloud storage services. Follow the Minio Client [Quickstart Guide](https://docs.minio.io/docs/minio-client-quickstart-guide) for further instructions.

README_zh_CN.md

@@ -84,7 +84,7 @@ go get -u github.com/minio/minio
 ## 使用Minio浏览器进行验证
 安装后使用浏览器访问[http://127.0.0.1:9000](http://127.0.0.1:9000)，如果可以访问，则表示minio已经安装成功。
 
-![Screenshot](https://github.com/minio/minio/blob/master/docs/screenshots/minio-browser.jpg?raw=true)
+![Screenshot](https://github.com/minio/minio/blob/master/docs/screenshots/minio-browser.png?raw=true)
 
 ## 使用Minio客户端 `mc`进行验证
 `mc` 提供了一些UNIX常用命令的替代品，像ls, cat, cp, mirror, diff这些。 它支持文件系统和亚马逊S3云存储服务。 更多信息请参考 [mc快速入门](https://docs.minio.io/docs/minio-client-quickstart-guide) 。