Missing bootstrap form classes on state and country select

[adamakhtar]

On the 3-0stable branch it seems only the country and state select boxes are missing .form-control classes which are required by bootstrap.

I don't know if this is intentional as I'm new to both Spree and this extension.

I forked the repo and made tiny adjustments and both the selects render correctly.

My adjustments can be seen here: adamakhtar@095166f

If you like I can merge this into 3-0stable and make a pull request.