There is no bubble-wrap 1.3.0.osx gem available. 

Changing the dependency to bubble-wrap 1.3.0 works fine on my OS X 1.8.3 setup

```Bundler could not find compatible versions for gem "bubble-wrap":
  In Gemfile:
    motion_model (>= 0) ruby depends on
      bubble-wrap (= 1.3.0.osx) ruby

    bubble-wrap (1.3.0)
```