README: update Apple App Store badge

Author: bk138

README.md

@@ -62,7 +62,7 @@ The roadmap for future developments regarding the project can be found
 ### MultiVNC for Desktop
 
 [<img src="https://flathub.org/api/badge?svg" height="60" />](https://flathub.org/apps/details/net.christianbeier.MultiVNC)
-[<img src="https://upload.wikimedia.org/wikipedia/commons/3/3c/Download_on_the_App_Store_Badge.svg" height="60" />](https://apps.apple.com/us/app/multivnc/id6738012997)
+[<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/3/3c/Download_on_the_App_Store_Badge.svg/320px-Download_on_the_App_Store_Badge.svg.png" height="60" />](https://apps.apple.com/us/app/multivnc/id6738012997)
 
 To get bleeding-edge packages built from the master development branch, navigate to
 [the list of CI runs](https://github.com/bk138/multivnc/actions/workflows/ci.yml),