Foundation: Fix bug one column OK

It's possible to have a unique column without defining size with Foundation.

This is OK:

    <div class="row">
        <div class="column"></div>
    </div>

But the next code block will give this error on each 'column' classes: <code>Foundation: When declaring column without size, only one element with the class 'column' (or 'columns') is allowed for a parent 'row' element.</code>

    <div class="row">
        <div class="column"></div>
        <div class="column"></div>
    </div>

This will close #1483