Fixed bad API call to jQuery.atr()

Not sure if this problem still exists upstream, but the buggy version makes '<a className="close"...' instead of '<a class="close"...'
Merge pull request #303 from davad/patch-1

Fixed bad API call to jQuery.attr()
Wrap data attributes in single quotes

To avoid breakage when passing along JSON serialized data.
Merge pull request #307 from vjt/patch-1

Wrap data attributes in single quotes