fix(CircleRoiTool.js): Extending hit area region within the circle boundary.
fix(CircleRoiTool.js): Extending hit area region within the circle boundary.

Previously, trying to highlight the circle from within the circle won't highlight the annotation.
This fix extends the hit area region towards the center from the boundary and thus allow to click
and drag the annotation as required.

fix #930

chafey/cornerstoneTools,cornerstonejs/cornerstoneTools,cornerstonejs/cornerstoneTools,cornerstonejs/cornerstoneTools