Update README.md

Author: malczuuu

README.md

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 # Problem4J Core
 
-[![](https://jitpack.io/v/malczuuu/problem4j-core.svg)](https://jitpack.io/#malczuuu/problem4j-core)
+[![JitPack](https://jitpack.io/v/malczuuu/problem4j-core.svg)](https://jitpack.io/#malczuuu/problem4j-core)
+[![Build Status](https://github.com/malczuuu/problem4j-jackson/actions/workflows/gradle.yml/badge.svg)](https://github.com/malczuuu/problem4j-jackson/actions/workflows/gradle.yml)
 
 > Part of [`problem4j`][problem4j] package of libraries.