Fix "undefined method 'perform' for main:Object" caused by merging #85.

Fix "undefined method 'perform' for main:Object" caused by merging #85.

```
NoMethodError: undefined method `perform' for main:Object
vendor/bundle/ruby/2.1.0/gems/bower-rails-0.8.1/lib/tasks/bower.rake:33:in `block (3 levels) in <top (required)>'`
```