message: Fix global assignment in Matomo plugin
diff: export default ({ router }) => {
  // Google analytics integration
  if (process.env.NODE_ENV === 'production' && typeof window !== 'undefined' && MATOMO_SITE_ID && MATOMO_TRACKER_URL) {
  - var _paq = _paq || [];
  + // We're in SSR space here, meaning that we have to explictly attach _paq to
  + // the window in order to store it globally.
  + if (window._paq == undefined) {
  + window._paq = [];
  + }
  + let _paq = window._paq;
  /* tracker methods like "setCustomDimension" should be called before "trackPageView" */
  _paq.push(['trackPageView']);
  if (MATOMO_ENABLE_LINK_TRACKING) {
  @@ -17,7 +22,8 @@ export default ({ router }) => {
  g.type='text/javascript'; g.async=true; g.defer=true; g.src=u+'piwik.js'; s.parentNode.insertBefore(g,s);
  })();
  router.afterEach(function (to) {
  - _paq.push(['trackPageView', to.fullPath]);
  + // Use window global here.
  + window._paq.push(['trackPageView', to.fullPath]);
  });
  }
  }
  