Use ctrl.$viewValue instead of element[0].value

I think it is completely wrong to use element[0].value.
If element is bound to a model which is an object (for example, Date object in datepickers) element[0].value is empty.
And correct way is to use $viewValue.
Update build
Merge pull request #51 from dmitry-dedukhin/patch-1

Use ctrl.$viewValue instead of element[0].value