fix(datepicker): change to dateDisabled

BREAKING CHANGE: Change validation key to `dateDisabled` to align better with Angular's convention

Author: wesleycho

Diff for: src/datepicker/datepicker.js

@@ -94,7 +94,7 @@ angular.module('ui.bootstrap.datepicker', ['ui.bootstrap.dateparser', 'ui.bootst
       this._refreshView();
 
       var date = ngModelCtrl.$viewValue ? new Date(ngModelCtrl.$viewValue) : null;
-      ngModelCtrl.$setValidity('date-disabled', !date || (this.element && !this.isDisabled(date)));
+      ngModelCtrl.$setValidity('dateDisabled', !date || (this.element && !this.isDisabled(date)));
     }
   };