fixing the CirclePageIndicator's chopped circles

When I used the `CirclePageIndicator`, I gave it a bigger radius, set the height to `wrap_contents` and experienced that the circles' top has 1px chopped. I modified it to measure the view 1 whateverunit taller, and broader, and start drawing with one more whateverunit offset.

Please review.

Another solution would be to draw differently, that might be better.