Update bk.js

lib/position/bk.js

@@ -1,7 +1,7 @@
 "use strict";
 
-var Graph = require("@dagrejs/graphlib").Graph;
-var util = require("../util");
+let Graph = require("@dagrejs/graphlib").Graph;
+let util = require("../util");
 
 /*
  * This module provides coordinate assignment based on Brandes and Köpf, "Fast
@@ -39,10 +39,10 @@ module.exports = {
  * single node in the layers being scanned.
  */
 function findType1Conflicts(g, layering) {
-  var conflicts = {};
+  let conflicts = {};
 
   function visitLayer(prevLayer, layer) {
-    var
+    let
       // last visited node in the previous layer that is incident on an inner
       // segment.
       k0 = 0,
@@ -53,13 +53,13 @@ function findType1Conflicts(g, layering) {
       lastNode = layer[layer.length - 1];
 
     layer.forEach((v, i) => {
-      var w = findOtherInnerSegmentNode(g, v),
+      let w = findOtherInnerSegmentNode(g, v),
         k1 = w ? g.node(w).order : prevLayerLength;
 
       if (w || v === lastNode) {
         layer.slice(scanPos, i+1).forEach(scanNode => {
           g.predecessors(scanNode).forEach(u => {
-            var uLabel = g.node(u),
+            let uLabel = g.node(u),
               uPos = uLabel.order;
             if ((uPos < k0 || k1 < uPos) &&
                 !(uLabel.dummy && g.node(scanNode).dummy)) {
@@ -80,10 +80,10 @@ function findType1Conflicts(g, layering) {
 }
 
 function findType2Conflicts(g, layering) {
-  var conflicts = {};
+  let conflicts = {};
 
   function scan(south, southPos, southEnd, prevNorthBorder, nextNorthBorder) {
-    var v;
+    let v;
     util.range(southPos, southEnd).forEach(i => {
       v = south[i];
       if (g.node(v).dummy) {