Update readme.

README.md

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 # 趣享GIF开源版 v1.0.3
 
-<img src="screenshots/giffun_demo.gif" width="300" align="right" hspace="20">
+<img src="screenshots/giffun_demo.gif" width="240" align="right" hspace="20">
 
 趣享GIF是一款Android端开源的GIF浏览和分享App，界面基于Material Design标准进行设计。App围绕GIF为主题，建立了一个小型的社交系统，在这里你可以：
 
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 <img src="screenshots/install_qrcode.png" width="180">
 
+---
 
 ### 屏幕截图
 
 <img src="screenshots/screenshot1.gif" width="25%" />
 <img src="screenshots/screenshot2.gif" width="25%" />
 <img src="screenshots/screenshot3.gif" width="25%" />
-<img src="screenshots/screenshot4.gif" width="25%" />
+<img src="screenshots/screenshot4.png" width="25%" />
 <img src="screenshots/screenshot5.png" width="25%" />
 <img src="screenshots/screenshot6.png" width="25%" />
 
+---
 
 ### License