fix: rank text seems not in the center of circle

[kurt-liao]

Hi, thanks for this wonderful project. I found that rank text looks not center of the circle, so I changed the cx and cy for the circle. You can see the effect after changed:

Before

After

I've created Stack Overflow stats card which also inspired by github-readme-stats. Just too happy to see your intersting project, so want to share mine with you😀.