Change text shadow color

When the background of the badge is not green, the text shadow looks a little weird (the change is easier to see in high resolution):

![badge_previous](https://f.cloud.github.com/assets/408035/2147564/2a1eea98-93d4-11e3-8dc2-d83ba78d02de.png)

With this fix, it looks better:

![badge_now](https://f.cloud.github.com/assets/408035/2147568/34e8514e-93d4-11e3-9ece-e92c89018b10.png)