修复无法跨设备创建硬链接bug

Archlinux/Centos运行报以下错误
```
 /tmp/repox8969815490132555300.tmp -> /home/jilen/.repox/storage: Invalid cross-device link 
 
java.nio.file.AtomicMoveNotSupportedException: /tmp/repox8969815490132555300.tmp -> /home/jilen/.repox/storage: Invalid cross-device link
	at sun.nio.fs.UnixCopyFile.move(UnixCopyFile.java:394) ~[na:1.8.0_25]
	at sun.nio.fs.UnixFileSystemProvider.move(UnixFileSystemProvider.java:262) ~[na:1.8.0_25]
	at java.nio.file.Files.move(Files.java:1395) ~[na:1.8.0_25]
	at com.gtan.repox.GetMaster$$anonfun$working$1.applyOrElse(GetMaster.scala:127) ~[com.gtan.repox-0.0.1.jar:0.0.1]
	at akka.actor.Actor$class.aroundReceive(Actor.scala:465) ~[com.typesafe.akka.akka-actor_2.11-2.3.7.jar:na]
	at com.gtan.repox.GetMaster.aroundReceive(GetMaster.scala:31) ~[com.gtan.repox-0.0.1.jar:0.0.1]
	at akka.actor.ActorCell.receiveMessage(ActorCell.scala:516) [com.typesafe.akka.akka-actor_2.11-2.3.7.jar:na]
	at akka.actor.ActorCell.invoke(ActorCell.scala:487) [com.typesafe.akka.akka-actor_2.11-2.3.7.jar:na]
	at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:254) [com.typesafe.akka.akka-actor_2.11-2.3.7.jar:na]
	at akka.dispatch.Mailbox.run(Mailbox.scala:221) [com.typesafe.akka.akka-actor_2.11-2.3.7.jar:na]
	at akka.dispatch.Mailbox.exec(Mailbox.scala:231) [com.typesafe.akka.akka-actor_2.11-2.3.7.jar:na]
	at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260) [org.scala-lang.scala-library-2.11.4.jar:na]
	at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339) [org.scala-lang.scala-library-2.11.4.jar:na]
	at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979) [org.scala-lang.scala-library-2.11.4.jar:na]
	at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107) [org.scala-lang.scala-library-2.11.4.jar:na]
21:19:12.547 DEBUG com.gtan.repox.GetMaster akka://repox/user/RequestQueueMaster/GetQueueWorker_956930504/GetMaster_-692253683 
```