Fix Readme

Author: akarnokd

README.md

@@ -6,7 +6,7 @@
 [![Maven Central](https://maven-badges.herokuapp.com/maven-central/com.github.akarnokd/rxjava3-interop/badge.svg)](https://maven-badges.herokuapp.com/maven-central/com.github.akarnokd/rxjava3-interop)
 
 RxJava 1.x: [![RxJava 1.x](https://maven-badges.herokuapp.com/maven-central/io.reactivex/rxjava/badge.svg)](https://maven-badges.herokuapp.com/maven-central/maven-central/io.reactivex/rxjava)
-RxJava 2.x: [![RxJava 3.x](https://maven-badges.herokuapp.com/maven-central/io.reactivex.rxjava3/rxjava/badge.svg)](https://maven-badges.herokuapp.com/maven-central/io.reactivex.rxjava3/rxjava)
+RxJava 3.x: [![RxJava 3.x](https://maven-badges.herokuapp.com/maven-central/io.reactivex.rxjava3/rxjava/badge.svg)](https://maven-badges.herokuapp.com/maven-central/io.reactivex.rxjava3/rxjava)
 
 Library to convert between RxJava 1.x and 3.x reactive types.