fix issue with Date.UTC

When running grunt test 
````
Running "jasmine:specs" (jasmine) task
Testing jasmine specs via phantom
........................................................................................................................................................................x...............................................................................................................................................................................................................................................................................
dc.compositeChart elastic chart axes should set the x domain: failed
  Expected false to be truthy. (1)
  Expected false to be truthy. (2)
440 specs in 4.073s.
>> 2 failures
Warning: Task "jasmine:specs" failed. Use --force to continue.
````