Can't upgrade sbt-native-packager...

all versions down to 0.7.0 fail with:

```
java.lang.RuntimeException: Error running chmod 0644 /localhome/jenkins/b/workspace/scala-release-2.11.x-unix/target/scala-2.11.5-1810ac0-nightly/usr/share/doc/scala/tools/images
	at scala.sys.package$.error(package.scala:27)
	at com.typesafe.sbt.packager.chmod$.apply(FileUtil.scala:11)
	at com.typesafe.sbt.packager.debian.DebianPlugin$$anonfun$debianSettings$21$$anonfun$apply$9$$anonfun$apply$11.apply(DebianPlugin.scala:159)
	at com.typesafe.sbt.packager.debian.DebianPlugin$$anonfun$debianSettings$21$$anonfun$apply$9$$anonfun$apply$11.apply(DebianPlugin.scala:157)
	at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
	at com.typesafe.sbt.packager.debian.DebianPlugin$$anonfun$debianSettings$21$$anonfun$apply$9.apply(DebianPlugin.scala:157)
	at com.typesafe.sbt.packager.debian.DebianPlugin$$anonfun$debianSettings$21$$anonfun$apply$9.apply(DebianPlugin.scala:152)
	at scala.collection.immutable.List.foreach(List.scala:318)
	at com.typesafe.sbt.packager.debian.DebianPlugin$$anonfun$debianSettings$21.apply(DebianPlugin.scala:152)
	at com.typesafe.sbt.packager.debian.DebianPlugin$$anonfun$debianSettings$21.apply(DebianPlugin.scala:149)
	at scala.Function9$$anonfun$tupled$1.apply(Function9.scala:35)
	at scala.Function9$$anonfun$tupled$1.apply(Function9.scala:34)
	at scala.Function1$$anonfun$compose$1.apply(Function1.scala:47)
	at sbt.$tilde$greater$$anonfun$$u2219$1.apply(TypeFunctions.scala:40)
	at sbt.std.Transform$$anon$4.work(System.scala:63)
	at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:226)
	at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:226)
	at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:17)
	at sbt.Execute.work(Execute.scala:235)
	at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:226)
	at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:226)
	at sbt.ConcurrentRestrictions$$anon$4$$anonfun$1.apply(ConcurrentRestrictions.scala:159)
	at sbt.CompletionService$$anon$2.call(CompletionService.scala:28)
	at java.util.concurrent.FutureTask.run(FutureTask.java:262)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
	at java.util.concurrent.FutureTask.run(FutureTask.java:262)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:745)
[error] (debian:debianExplodedPackage) Error running chmod 0644 /localhome/jenkins/b/workspace/scala-release-2.11.x-unix/target/scala-2.11.5-1810ac0-nightly/usr/share/doc/scala/tools/images
```

https://scala-webapps.epfl.ch/jenkins/job/scala-release-2.11.x-unix/180/console