*
@method getUTCOffset([iso])
@returns String
@short Returns a string representation of the offset from UTC time. If [iso] is true the offset will be in ISO8601 format.
@example

new Date().getUTCOffset()     -> "+0900"
new Date().getUTCOffset(true) -> "+09:00"

*
function(iso) {
      var offset = this._utc ? 0 : this.getTimezoneOffset();
      var colon  = iso === true ? ':' : '';
      if(!offset && iso) return 'Z';
      return padNumber(floor(-offset / 60), 2, true) + colon + padNumber(math.abs(offset % 60), 2);
    }