feat: disallow call Redis() as a function

BREAKING CHANGE:
The `new` keyword is required explicitly. So `Redis(/* options */)`
will not work, use `new Redis(/* options */)` instead.

lib/redis.js

@@ -91,7 +91,6 @@ var PromiseContainer = require('./promise_container');
  * var Redis = require('ioredis');
  *
  * var redis = new Redis();
- * // or: var redis = Redis();
  *
  * var redisOnPort6380 = new Redis(6380);
  * var anotherRedis = new Redis(6380, '192.168.100.1');
@@ -103,10 +102,6 @@ var PromiseContainer = require('./promise_container');
  * ```
  */
 function Redis() {
-  if (!(this instanceof Redis)) {
-    return new Redis(arguments[0], arguments[1], arguments[2]);
-  }
-
   this.parseOptions(arguments[0], arguments[1], arguments[2]);
 
   EventEmitter.call(this);
@@ -139,8 +134,8 @@ Object.assign(Redis.prototype, Commander.prototype);
  *
  * @deprecated
  */
-Redis.createClient = function () {
-  return Redis.apply(this, arguments);
+Redis.createClient = function (...args) {
+  return new Redis(...args);
 };
 
 /**

test/unit/redis.js

@@ -82,8 +82,8 @@ describe('Redis', function () {
       }
       Redis.prototype.connect.restore();
 
-      function getOption() {
-        var redis = Redis.apply(null, arguments);
+      function getOption(...args) {
+        var redis = new Redis(...args);
         return redis.options;
       }
     });