Substitue backtick with a single quote

Otherwise if I tried:

```bash
rails_apps_composer new . -r core
```
 I would get:

```bash
.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rails_apps_composer-3.0.28/lib/rails_wizard/recipe.rb:30:in `split': invalid byte sequence in US-ASCII (ArgumentError)
```