Remove inline-block fallback for IE <= 7

Because the original `span` element is `display: inline`, it doesn't need a fallback for `inline-block`. Plus, this fallback was causing some alignment issues in IE's compatibility mode.

I haven't re-run the Grunt build because my computer at work doesn't have Node installed (this also means I haven't actually tested this change yet). I thought I'd at least get the PR set up so you can take a look and see if this seems like an appropriate approach.  When finished, this will fix #304.