accessing the correct properties in dataRange

+ replaced property name 'start' to 'min'
+ replaced property name 'end' to 'max'

lib/timeline/Core.js

@@ -459,7 +459,7 @@ Core.prototype.getVisibleItems = function() {
 Core.prototype.fit = function(options) {
   var range = this.getDataRange();
 
-  // skip range set if there is no start and end date
+  // skip range set if there is no min and max date
   if (range.min === null && range.max === null) {
     return;
   }