Fix StatisticsPage() invocation

ai-simplesitestats.php

@@ -119,7 +119,7 @@ class AiSSS {
     }
 
     public function addStatsPage() {
-        $statsPage = new AI_SSS\Statistics($this);
+        $statsPage = new StatisticsPage($this);
         $statsPageId = add_dashboard_page(
             __('Statistics', 'ai-simplesitestats'),
             'Stats',