Improve the version badge - make it link to Scaladex.

Author: sageserpent-open

README.markdown

@@ -1,8 +1,7 @@
 # Americium - **_Test cases galore! Automatic case shrinkage! Bring your own test style. For Scala and Java..._**
 
 [![Build Status](https://travis-ci.com/sageserpent-open/americium.svg?branch=master)](https://travis-ci.com/sageserpent-open/americium)
-[![Maven Central](https://maven-badges.herokuapp.com/maven-central/com.sageserpent/americium_2.13/badge.svg?style=flat&gav=true)](https://maven-badges.herokuapp.com/maven-central/com.sageserpent/americium_2.13/badge.svg)
-[![Maven Central](https://maven-badges.herokuapp.com/maven-central/com.sageserpent/americium_3/badge.svg?style=flat&gav=true)](https://maven-badges.herokuapp.com/maven-central/com.sageserpent/americium_3/badge.svg)
+[![Maven Central](https://index.scala-lang.org/sageserpent-open/americium/americium/latest-by-scala-version.svg?color=2465cd&style=flat)](https://index.scala-lang.org/sageserpent-open/americium/americium)
 
 ## What? Why? ##