Use SVG badges

[tagliala]

[ci skip]

Before and after:

[ariejan]

@oestrich seems ok to me. Can I help out with handling issues / pull requests?

[oestrich]

I'm fine merging this, but is there a reason for svg vs what we have now? Since they look the same.

[tagliala]

Hi,

.png badges look different in both height, background-color and font weight

Maybe a screenshot with a retina display shows the differences better

(before -> after)

[oestrich]

Thanks!