Declare constants with const keyword

lib/cartodb/models/dataview/aggregation.js

@@ -131,9 +131,9 @@ const aggregationQueryTpl = ctx => `
     ORDER BY value DESC
 `;
 
-var CATEGORIES_LIMIT = 6;
+const CATEGORIES_LIMIT = 6;
 
-var VALID_OPERATIONS = {
+const VALID_OPERATIONS = {
     count: [],
     sum: ['aggregationColumn'],
     avg: ['aggregationColumn'],
@@ -141,7 +141,7 @@ var VALID_OPERATIONS = {
     max: ['aggregationColumn']
 };
 
-var TYPE = 'aggregation';
+const TYPE = 'aggregation';
 
 /**
  {