Match actual extension in .icon-tab() and .icon-tree()

Use the `$=` syntax instead of `*=` to match the extension against the end of the `data-name` value. This way the actual extension is matched rather than any part of the `data-name`.

I am not sure if there is any reason why you aren’t doing it this way. I didn’t see any breakage when I made this change to my local build.