I think you need to use the `licenses` attribute here, otherwise we can't build the gem.

```
~/code/ptec/devise | 2.0.0-p0 (reneedv-master)
$ rake install
rake aborted!
ERROR:  While executing gem ... (Gem::InvalidSpecificationException)
    licenses must be an Array of String

Tasks: TOP => install => build
(See full trace by running task with --trace)
```