added explicitly set locale on NSDateFormatters to bypass Apple bug.

There is a know NSDateFormatter bug the causes date parse to fail on this document in some cases. The bug happens in some cases when the user sets a different locale other than 'en_US'. The bug causes NSDateFormatter to expect an am/pm even when sent to parse 24hr strings. This is easily solved by explicitly setting the locale of the NSDateFormatter.
Merge pull request #258 from AndresCanella/patch-1

added explicitly set locale on NSDateFormatters to bypass Apple bug.