'let' => 'var' in client JS

views/statistics.ejs

@@ -15,7 +15,7 @@ let types = {
 <script src="/libs/morris.js/morris.min.js"></script>
 <script>
 function getColorOfScore(score) {
-  let color = [];
+  var color = [];
   color[0] = 'red';
   color[1] = '#ff4b00';
   color[2] = '#ff6200';