function errorSync(err, plugins, manager, token) {
  plugins
    .filter(hasMethod('onError'))
    .forEach((plugin) => plugin.onError(manager.contextFor(plugin, token), err));
}
Iterates through the plugins and calls the specified synchronous `onError` handler
(when present).

Passes in the appropriate context object, as well as the error.

@param {Error} err
@param {Array<HypernovaPlugin>} plugins
@param {BatchManager} manager
@param {String} [token]