Python build broken

[FRosner]

https://travis-ci.org/FRosner/drunken-data-quality/jobs/316831716

.......java.util.concurrent.RejectedExecutionException: Task scala.concurrent.impl.CallbackRunnable@60c5b9bf rejected from java.util.concurrent.ThreadPoolExecutor@5143e6eb[Shutting down, pool size = 1, active threads = 1, queued tasks = 0, completed tasks = 0]
	at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2063)
	at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:830)
	at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1379)
	at scala.concurrent.impl.ExecutionContextImpl$$anon$1.execute(ExecutionContextImpl.scala:136)
	at scala.concurrent.impl.CallbackRunnable.executeWithValue(Promise.scala:40)
	at scala.concurrent.impl.Promise$DefaultPromise.tryComplete(Promise.scala:248)
	at scala.concurrent.Promise$class.complete(Promise.scala:55)
	at scala.concurrent.impl.Promise$DefaultPromise.complete(Promise.scala:153)
	at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:23)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
java.util.concurrent.RejectedExecutionException: Task scala.concurrent.impl.CallbackRunnable@71ac7561 rejected from java.util.concurrent.ThreadPoolExecutor@5143e6eb[Shutting down, pool size = 1, active threads = 1, queued tasks = 0, completed tasks = 0]
	at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2063)
	at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:830)
	at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1379)
	at scala.concurrent.impl.ExecutionContextImpl$$anon$1.execute(ExecutionContextImpl.scala:136)
	at scala.concurrent.impl.CallbackRunnable.executeWithValue(Promise.scala:40)
	at scala.concurrent.impl.Promise$DefaultPromise.tryComplete(Promise.scala:248)
	at scala.concurrent.Promise$class.complete(Promise.scala:55)
	at scala.concurrent.impl.Promise$DefaultPromise.complete(Promise.scala:153)
	at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:23)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)