Add stroke, fill etc. SVG prop enhancers

[brandongregoryscott]

In testing segmentio/evergreen#1554, I noticed the loading animation for the Spinner isn't quite right because we aren't handling the stroke* properties it is setting:

https://github.com/segmentio/evergreen/pull/1554/files#diff-785b18b0b236f691ca4ccc4f4ce95194404c83218c58a9229ac386f07a403dd3R15-R22

Current	Expected

I think we'll want at least these css properties:

• fill
• strokeDashoffset
• strokeDasharray
• strokeWidth
• strokeMiterlimit
• strokeLinecap
• stroke