Fixed F-Droid badge

Author: mkulesh

README.md

@@ -11,7 +11,7 @@ This app is not only for students. Anyone who enjoys mathematics or requires mor
 
 [<img src="https://play.google.com/intl/en_us/badges/images/generic/en_badge_web_generic.png"
       alt="Get it on Google Play" height="110">](https://play.google.com/store/apps/details?id=com.mkulesh.micromath.plus)
-[<img src="https://gitlab.com/fdroid/artwork/raw/master/badge/get-it-on.png"
+[<img src="https://fdroid.gitlab.io/artwork/badge/get-it-on.png"
       alt="Get it on F-Droid" height="110">](https://f-droid.org/packages/com.mkulesh.micromath.plus)
 
 ## Benefits and features: