Negative test not working for file hashing

refer - https://github.com/oclif/oclif/issues/142

![image](https://user-images.githubusercontent.com/16856802/67241606-5cfbd300-f471-11e9-925e-de19ffa1e8e9.png)

![image](https://user-images.githubusercontent.com/16856802/67241828-d398d080-f471-11e9-98af-8fcba577448a.png)
