Modified readme

Author: coderatio

README.md

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 # Simple-backup
-<img src="/_docs/store_export.png"/><br/>
+<img src="/_docs/store_export.PNG"/><br/>
 A simple mysql database backup library for php. This library helps you backup your mysql database to a directory in your project or download it to your machine. 
 
 The library also allows you import or restore a database without stress. Follow the instructions below to get started.