Apply prefer-const lint rule

lib/versioned-map.js

@@ -142,7 +142,7 @@ class VersionedMap {
 
     var res = {};
 
-    for (let i in v) {
+    for (const i in v) {
       if (v[i] === NONEXISTENT) res.delete |= 1 << i;
       else res[i] = v[i];
     }
@@ -154,11 +154,11 @@ class VersionedMap {
     var del = 0;
     var rev = [];
     var minKey = 999;
-    for (let k in revisions) {
+    for (const k in revisions) {
       if (k === "delete") {
         del = revisions[k];
       } else {
-        let r = parseInt(k);
+        const r = parseInt(k);
         minKey = Math.min(minKey, r);
         for (let i = this._sizeDiff.length; i <= r; ++i)
           this._sizeDiff[i] = this._sizeDiff[i - 1];
@@ -195,8 +195,8 @@ class VersionedMap {
   }
 
   *diff() {
-    for (let pair of this.map) {
-      let current = pair[1][pair[1].length - 1];
+    for (const pair of this.map) {
+      const current = pair[1][pair[1].length - 1];
       if (current === NONEXISTENT) {
         if (0 in pair[1]) yield [pair[0], pair[1][0]];
         else yield [pair[0]];
@@ -216,14 +216,14 @@ class VersionedMap {
     this._sizeDiff[revision] = this._sizeDiff[this._sizeDiff.length - 1];
     this._sizeDiff.splice(revision + 1, this._sizeDiff.length);
 
-    let d = this.dirty >> revision;
+    const d = this.dirty >> revision;
     this.dirty = this.dirty ^ (d << revision);
     this.dirty |= +!!d << revision;
 
-    for (let pair of this.map) {
-      let k = pair[0];
-      let v = pair[1];
-      let last = v[v.length - 1];
+    for (const pair of this.map) {
+      const k = pair[0];
+      const v = pair[1];
+      const last = v[v.length - 1];
       if (last === NONEXISTENT) {
         v.splice(revision, v.length);
         if (v.some(() => true)) v[revision] = NONEXISTENT;