Bugfix: date filter now correctly formats high precision date-times

Fix the date filter so fractional seconds are processed correctly. For example ``{{2003-09-10T13:02:03.987654Z | date: yyyy-mm-dd ss}}``` is now formatted as ```2003-09-10 03``.

Prior to this fix it was formatted as ```2003-09-10 30``` because the code treated ```.987654``` as 987.654s / 60s = 16 minutes 27.654 seconds so 27 seconds were added to the second component of the date.

See:
https://github.com/angular/angular.js/pull/989. See https://github.com/steinjak/angular.js/commit/2df31b5e4c1e23461b62ecf9789645bcfc3451c5.

The original code did not handle fractions of a second correctly. For example ```{{2003-09-10T13:02:03.987654Z | date: yyyy-mm-dd ss}}``` would be formatted as "2003-09-10 19" because the code assumed there were 987.654ms, so 987/60=16 seconds were added to the date/time.

This pull request correctly formats the