message: interact: simplify "use" method
  - tags just one plugin
  - plugin object must have an "init" method
diff: @@ -49,18 +49,13 @@ function interact (element, options) {
  *
  * @alias module:interact.use
  *
  - * @param {...function | ...array} plugins
  + * @param {Object} plugin
  + * @param {function} plugin.init
  * @return {interact}
  */
  -interact.use = function (...plugins) {
  - for (const plugin of plugins) {
  - if (utils.is.array(plugin)) {
  - interact.use(...plugin);
  - }
  - else {
  - (plugin.init || plugin)(scope);
  - }
  - }
  +interact.use = function (plugin) {
  + plugin.init(scope);
  + return interact;
  };
  /**
  