Can't use RouteRest: java.lang.NoClassDefFoundError: Failed resolution of: Lrx/util/async/Async;

[emanueleDiVizio]

No idea what causes this, i'll report the stacktrace below.

java.lang.NoClassDefFoundError: Failed resolution of: Lrx/util/async/Async;
 at com.github.polok.routedrawer.RouteRest.getJsonDirections(RouteRest.java:60)

Caused by: java.lang.ClassNotFoundException: Didn't find class "rx.util.async.Async" on path: DexPathList[[zip file "/data/app/packagename/base.apk"],nativeLibraryDirectories=[/vendor/lib, /system/lib]]
            at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
            at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
            at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
            at com.github.polok.routedrawer.RouteRest.getJsonDirections(RouteRest.java:60)