code: function(callback) {
      return WebApiRequest.builder(this.getAccessToken())
        .withPath('/v1/me/player/previous')
        .withHeaders({ 'Content-Type': 'application/json' })
        .build()
        .execute(HttpManager.post, callback);
    }
docs: Skip the Current User's Playback To Previous Track
  @param {requestCallback} [callback] Optional callback method to be called instead of the promise.
  @example playbackPrevious().then(...)
  @returns {Promise|undefined} A promise that if successful, resolves into a paging object of tracks,
  otherwise an error. Not returned if a callback is given.