adjusting minimal node size

Author: monfera

src/traces/sankey/render.js

@@ -182,7 +182,7 @@ function nodeModel(uniqueKeys, d, n) {
         zoneThicknessPad = c.nodePadAcross,
         zoneLengthPad = d.nodePad / 2,
         visibleThickness = n.dx,
-        visibleLength = Math.max(1, n.dy);
+        visibleLength = Math.max(0.5, n.dy);
 
     var basicKey = n.label;
     var foundKey = uniqueKeys[basicKey];