Use const keyword for constants

lib/cartodb/models/dataview/histogram.js

@@ -44,10 +44,6 @@ const dateIntervalQueryTpl = ctx => `
     FROM __cdb_interval_in_days, __cdb_interval_in_hours, __cdb_interval_in_minutes, __cdb_interval_in_seconds
 `;
 
-var MAX_INTERVAL_VALUE = 366;
-var BIN_MIN_NUMBER = 6;
-var BIN_MAX_NUMBER = 48;
-
 const filterOutSpecialNumericValues = ctx => `
         ${ctx._column} != 'infinity'::float
     AND
@@ -285,7 +281,22 @@ const dateHistogramQueryTpl = ctx => `
     ORDER BY bin
 `;
 
-var TYPE = 'histogram';
+const MAX_INTERVAL_VALUE = 366;
+const BIN_MIN_NUMBER = 6;
+const BIN_MAX_NUMBER = 48;
+
+const TYPE = 'histogram';
+
+const DATE_AGGREGATIONS = {
+    'auto': true,
+    'minute': true,
+    'hour': true,
+    'day': true,
+    'week': true,
+    'month': true,
+    'quarter': true,
+    'year': true
+};
 
 /**
 Numeric histogram:
@@ -721,14 +732,3 @@ module.exports = class Histogram extends BaseWidget {
         return '' + offsetInHours;
     }
 };
-
-var DATE_AGGREGATIONS = {
-    'auto': true,
-    'minute': true,
-    'hour': true,
-    'day': true,
-    'week': true,
-    'month': true,
-    'quarter': true,
-    'year': true
-};