I tried using the JAR available for download and it didn't work either. To get this working, I had to download the project available at github here. Compile and run the task "makeJar" (right click on task makeJar in the gradle.build and select run).
I just added this new jar in the libs and referenced in the gradle.build file.
dependencies {
...
compile files('libs/RootTools.jar')
}
or you can add it via Project Properties.
It worked perfectly (don't forget to sync your the gradle files if you edit it manually).