feat: update ts solution to lc problem: No.637 (doocs#2619)

Author: thinkasany

solution/0600-0699/0637.Average of Levels in Binary Tree/README.md

@@ -245,8 +245,8 @@ impl Solution {
  * @return {number[]}
  */
 var averageOfLevels = function (root) {
-    let q = [root];
-    let ans = [];
+    const q = [root];
+    const ans = [];
     while (q.length) {
         const n = q.length;
         let s = 0;

solution/0600-0699/0637.Average of Levels in Binary Tree/README_EN.md

@@ -235,8 +235,8 @@ impl Solution {
  * @return {number[]}
  */
 var averageOfLevels = function (root) {
-    let q = [root];
-    let ans = [];
+    const q = [root];
+    const ans = [];
     while (q.length) {
         const n = q.length;
         let s = 0;

solution/0600-0699/0637.Average of Levels in Binary Tree/Solution.js

@@ -11,8 +11,8 @@
  * @return {number[]}
  */
 var averageOfLevels = function (root) {
-    let q = [root];
-    let ans = [];
+    const q = [root];
+    const ans = [];
     while (q.length) {
         const n = q.length;
         let s = 0;