Index: node_modules/d3-hierarchy/src/hierarchy/sum.js
===================================================================
--- node_modules/d3-hierarchy/src/hierarchy/sum.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
+++ node_modules/d3-hierarchy/src/hierarchy/sum.js	(revision e4c61dd6cd86e06265bc2bd91adba84a0f04044a)
@@ -0,0 +1,9 @@
+export default function(value) {
+  return this.eachAfter(function(node) {
+    var sum = +value(node.data) || 0,
+        children = node.children,
+        i = children && children.length;
+    while (--i >= 0) sum += children[i].value;
+    node.value = sum;
+  });
+}