Bug fix for OAuth token generation in IRB console

I had a problem generating an OAuth token using the IRB console and after some research, found [this post](https://groups.google.com/d/msg/tumblr-api/foJZZdSKO2s/IeX5DyCOtmsJ), explaining that OOB is not supported by the API. Although the API most likely never supported OOB, it seems that until recently, it didn't complain. I made a simple change to fix the issue.