allow stroke width less than 0.1

**Is your feature request related to a problem? Please describe.**

We are going to use kepler.gl for microscale geographic data, floor plan. And we think kepler.gl is really promising platform. But it's minimum stroke width is 0.1 and line drawings looks not so good with that think strokes. Currently, if we set the stroke value less than 0.1, then the UI automatically sets it to 0.1. (It seems that stroke width control slider's incremental step is set to 0.1)

**Describe the solution you'd like**
Please allow stroke width less than 0.1, or decrease the slide step from 0.1 to 0.01 or 0.02.

**Additional context**
If this issue fixed, kepler.gl can be an excellent information visualization tool for architecture industry.