Smaller inner border radius.

This makes the issue in https://github.com/CloudMade/Leaflet/issues/1214 better. I only say better, because it can still look a bit bad on a dark map (as can be seen below), but it's much better at least!

![Screen Shot 2012-12-12 at 19 04 05 ](https://f.cloud.github.com/assets/1341313/8794/8e3f0092-4486-11e2-9a6a-b06996dc56d0.png)