Replace obsolete Bintray badge with Scaladex version (#1431)
Replace obsolete Bintray badge with Scaladex version (#1431)

Unfortunately the Bintray badge on the readme is broken, I guess due to Bintray being [sunset](https://jfrog.com/blog/into-the-sunset-bintray-jcenter-gocenter-and-chartcenter/)? However, this new Scaladex badge can replace the old Bintray badge - it summarises which versions of sbt are supported by sbt-native-packager (and what the latest sbt-native-packager version is for each of those sbt versions):

[![sbt-native-packager Scala version support](https://index.scala-lang.org/sbt/sbt-native-packager/sbt-native-packager/latest-by-scala-version.svg?targetType=Sbt)](https://index.scala-lang.org/sbt/sbt-native-packager/sbt-native-packager)

More details on the badge format here: https://github.com/scalacenter/scaladex/pull/660 (with some extra changes to better support sbt in https://github.com/scalacenter/scaladex/pull/674).
sbt/sbt-native-packager,sbt/sbt-native-packager,sbt/sbt-native-packager,sbt/sbt-native-packager,sbt/sbt-native-packager,sbt/sbt-native-packager