Apply prefer-const lint rule

lib/cache.js

@@ -142,17 +142,17 @@ function redisLock(lockName, ttl, callback) {
 }
 
 function mongoGet(key, callback) {
-  let expire = new Date(Date.now() - mongoTimeOffset);
+  const expire = new Date(Date.now() - mongoTimeOffset);
   if (Array.isArray(key)) {
     mongoCollection.find({ _id: { $in: key } }).toArray((err, res) => {
       if (err) return void callback(err);
 
-      let indices = {};
+      const indices = {};
       key.forEach((v, i) => {
         indices[v] = i;
       });
 
-      let values = [];
+      const values = [];
       res.forEach(r => {
         if (r["expire"] > expire) values[indices[r["_id"]]] = r["value"];
       });
@@ -183,7 +183,7 @@ function mongoSet(key, value, ttl, callback) {
 
   if (!ttl) ttl = MAX_CACHE_TTL;
 
-  let expire = new Date(Date.now() - mongoTimeOffset + ttl * 1000);
+  const expire = new Date(Date.now() - mongoTimeOffset + ttl * 1000);
   mongoCollection.save({ _id: key, value: value, expire: expire }, callback);
 }
 
@@ -216,7 +216,7 @@ function mongoLock(lockName, ttl, callback) {
           throw err || new Error("Lock expired");
       });
     } else {
-      let expire = new Date(Date.now() - mongoTimeOffset + extendTtl * 1000);
+      const expire = new Date(Date.now() - mongoTimeOffset + extendTtl * 1000);
       mongoCollection.update(
         { _id: lockName, value: token },
         { expire: expire },
@@ -228,8 +228,8 @@ function mongoLock(lockName, ttl, callback) {
     }
   }
 
-  let expireTest = new Date(Date.now() - mongoTimeOffset);
-  let expireSet = new Date(Date.now() - mongoTimeOffset + ttl * 1000);
+  const expireTest = new Date(Date.now() - mongoTimeOffset);
+  const expireSet = new Date(Date.now() - mongoTimeOffset + ttl * 1000);
 
   mongoCollection.update(
     { _id: lockName, expire: { $lte: expireTest } },