Update main image to better handle dark background

Fixes #1880

Co-authored-by: Deleplace <deleplace2015@gmail.com>
Signed-off-by: Marc Khouzam <marc.khouzam@gmail.com>

README.md

@@ -1,4 +1,4 @@
-![cobra logo](https://cloud.githubusercontent.com/assets/173412/10886352/ad566232-814f-11e5-9cd0-aa101788c117.png)
+![cobra logo](https://user-images.githubusercontent.com/13508141/208113069-6bdccb85-1797-4946-9fff-c35443fbb29e.png)
 
 Cobra is a library for creating powerful modern CLI applications.