code: function adjustNodeHeight (node, dy, sankeyY0, sankeyY1) {
      if ((node.y0 + dy >= sankeyY0) && (node.y1 + dy <= sankeyY1)) {
        node.y0 = node.y0 + dy
        node.y1 = node.y1 + dy
  
        node.targetLinks.forEach(function (l) {
          l.y1 = l.y1 + dy
        })
  
        node.sourceLinks.forEach(function (l) {
          l.y0 = l.y0 + dy
        })
      }
      return node
    }
docs: update a node, and its associated links, vertical positions (y0, y1)