Dependent of rails ">= 3.1", "< 5.0" will work with rails 4.*

Hi. rails-canonical with rails4.0.0.beta1 raise an error:

```
Bundler could not find compatible versions for gem "rails":
  In Gemfile:
    canonical-rails (>= 0) ruby depends on
      rails (~> 3.1) ruby

    rails (4.0.0.beta1)
```