fix issue with JNI libraries for sbt 0.13, refs #36

Hi,

I had the same issue described in #36, since 0.13 sbt does forking a bit different, see

https://github.com/sbt/sbt/blob/473fc8476d25ef3fcbfe6b91b7ee57f1099bdf72/main/src/main/scala/sbt/Defaults.scala#L453
https://github.com/sbt/sbt/blob/9c442d3aed53bdc89db1ada9d5b204bf02adb339/run/src/main/scala/sbt/Run.scala#L26

You can verify this fix by launching any akka-persistence application with native leveldb journal.

Thanks,
Gleb