rack should be a regular dependency, not a development dependency

Hi,

I'm using localeapp in a project which does not include rack.

`bundle exec localeapp --help` fails with the following error:

````
/Users/martin/.gem/gems/localeapp-0.6.9/lib/localeapp/routes.rb:1:in `require': cannot load such file -- rack/utils (LoadError)
	from /Users/martin/.gem/gems/localeapp-0.6.9/lib/localeapp/routes.rb:1:in `<top (required)>'
	from /Users/martin/.gem/gems/localeapp-0.6.9/lib/localeapp.rb:28:in `require'
	from /Users/martin/.gem/gems/localeapp-0.6.9/lib/localeapp.rb:28:in `<top (required)>'
	from /Users/martin/.gem/gems/localeapp-0.6.9/bin/localeapp:4:in `require'
	from /Users/martin/.gem/gems/localeapp-0.6.9/bin/localeapp:4:in `<top (required)>'
	from /Users/martin/.gem/bin/localeapp:23:in `load'
	from /Users/martin/.gem/bin/localeapp:23:in `<main>'
```

This pull request fixes the problem.