EUCA-7478
Rivets patch provided by Adam Heath <doogie@brainfood.com>

The attached simple patch should fix the following issue with rivets:
<div class="foo bar" data-class-baz="variable"></div>
When baz becomes truthy, rivets would remove 'foo bar' from the class.
Merge pull request #34 from eucalyptus/adamh/dev/EUCA-7478

Adamh/dev/euca 7478