Allow stroke width to go to 0. Fixes #14.

lib/svg-symbol.tsx

@@ -72,7 +72,7 @@ function reactifySvgSymbolElement(
   let vectorEffect;
   fill = getColor(ctx, fill);
   stroke = getColor(ctx, stroke);
-  if (strokeWidth !== undefined && ctx.uniformStrokeWidth) {
+  if (strokeWidth !== undefined && typeof ctx.uniformStrokeWidth === "number") {
     strokeWidth = ctx.uniformStrokeWidth;
     vectorEffect = "non-scaling-stroke";
   }

lib/symbol-context-widget.tsx

@@ -42,7 +42,7 @@ export const SymbolContextWidget: React.FC<{
           <label htmlFor="strokeWidth">Stroke width: </label>
           <input
             type="range"
-            min={0.5}
+            min={0}
             max={3}
             step={0.1}
             value={ctx.uniformStrokeWidth}