Make sure info about versions is included for cached events

This commit modifies trackCachedEvents() to call track() instead of window.mixpanel.track().

This is needed to make sure that we include information about the free
and premium versions (which is done inside track()) for cached events
(events that were added before mixpanel loaded).

[MAILPOET-3885]

assets/js/src/analytics_event.js

@@ -50,7 +50,7 @@ function exportMixpanel() {
 function trackCachedEvents() {
   eventsCache.forEach(function trackIfEnabled(event) {
     if (window.mailpoet_analytics_enabled || event.forced) {
-      window.mixpanel.track(event.name, event.data);
+      track(event.name, event.data);
     }
   });
 }