More specific modal delete button selector.

Was [breaking tests](http://ci.reciprocitylabs.com:8080/job/Automated%20Test%20Battery%20DEV/171/) 2/14/14 because a recent [commit](https://github.com/reciprocity/ggrc-core/commit/7b97dbc5) made it so the selector would find the "close" button instead of the "delete" button.  Fixed with a more specific selector that will not grab anything with "danger" in the `class`.