Bundler plugin: Unknown switches '--jobs=4'

If "bundler" plugin enabled and run ```bi``` shortcut, Bundler throws exception:

```
~/projects/rails_project$ bi                                                                                                            
Unknown switches '--jobs=4'
```

My environment:
```
Ruby 2.1.0dev (2013-10-11) [x86_64-darwin11.4.2]
Bundler version 1.3.5
```

The parallel gem installations ('--jobs=N') is feature in Bundler 1.4.0.pre.1,
so I think plugin should detect version for this option,
or there is no need in this feature.

What you think?