:art: Don't output the .loading class for spinners
:art: Don't output the .loading class for spinners

since `.loading` get's used in other contexts and not just for the spinner.

Part of https://github.com/atom/one-dark-ui/pull/88

torx-io/torx-dark-ui,torx-io/torx-dark-ui,torx-io/torx-dark-ui,torx-io/torx-dark-ui,torx-io/torx-dark-ui,torx-io/torx-dark-ui,torx-io/torx-dark-ui