updated Video2X banner to be compatible with GitHub's new dark theme

Author: k4yt3x

README.md

@@ -1,5 +1,5 @@
 <p align="center">
-   <img src="https://user-images.githubusercontent.com/21986859/81626588-ae5ab800-93eb-11ea-918f-ebe98c2de40a.png"/>
+   <img src="https://user-images.githubusercontent.com/21986859/102733190-872a7880-4334-11eb-8e9e-0ca747f130b1.png"/>
 </p>
 
 ![GitHub release (latest by date)](https://img.shields.io/github/v/release/k4yt3x/video2x?style=flat-square)