changed private property name

lib/event-tracker.js

@@ -25,19 +25,19 @@ class EventTracker{
         this.db = new Database(filename);
         this.appCurrentState = AppState.currentState;
         this._handleAppStateChange = this._handleAppStateChange.bind(this);
-        this._appFocused = false;
+        this._focus = false;
     }
 
     get isFocused() {
-        return this._appFocused;
+        return this._focus;
     }
 
     /**
      * @param {boolean} bool
      */
     set setFocus(bool) {
         if(typeof bool !== 'boolean') return;
-        this._appFocused = bool;
+        this._focus = bool;
     }
     /**
      * Adds an event to the database after performing validations.