pauseTrack ({ state, dispatch }, track) {
      const trackData = state.tracks[track]
      if (!trackData) {
        throw new Error('Invalid track specified')
      }

      const pauses = Array.from(trackData.keys())
        .map(id => dispatch('pauseSound', id))

      return Promise.all(pauses)
    }
Pauses the specified track.  Track must be valid.
Noop when already paused

@param track {string} name of track to pause
@throws {Error} when invalid track specified