track APPLICATION_UPGRADED in Mixpanel

Author: maxme

WordPressAnalytics/src/main/java/org/wordpress/android/analytics/AnalyticsTrackerMixpanel.java

@@ -261,6 +261,10 @@ private AnalyticsTrackerMixpanelInstructionsForStat instructionsForStat(
                 instructions = AnalyticsTrackerMixpanelInstructionsForStat.
                         mixpanelInstructionsForEventName("Application Closed");
                 break;
+            case APPLICATION_UPGRADED:
+                instructions = AnalyticsTrackerMixpanelInstructionsForStat.
+                        mixpanelInstructionsForEventName("Application Upgraded");
+                break;
             case THEMES_ACCESSED_THEMES_BROWSER:
                 instructions = AnalyticsTrackerMixpanelInstructionsForStat.
                         mixpanelInstructionsForEventName("Themes - Accessed Theme Browser");