Update README_CN.md

Author: lizhuoyuan

README_CN.md

@@ -19,7 +19,7 @@
 [更新日志](https://github.com/OpenFlutter/flutter_screenutil/blob/master/CHANGELOG.md)
 
 ## Note
-[v3](https://github.com/OpenFlutter/flutter_screenutil/tree/beta)可用于`flutter> = 1.19.0`
+[v3](https://github.com/OpenFlutter/flutter_screenutil/tree/beta)可用于`flutter> = 1.19.0`  
 [v2](https://github.com/OpenFlutter/flutter_screenutil)用于当前Flutter的`stable`版本。
 
 ## 使用方法: