added duplicate function to redis

redis/redis-tests.ts

@@ -111,4 +111,7 @@ client.multi(commandArr).exec();
 client.monitor(resCallback);
 
 // Send command
-client.send_command(str, args, resCallback);
+client.send_command(str, args, resCallback);
+
+// Duplicate
+client.duplicate();

redis/redis.d.ts

@@ -386,6 +386,9 @@ declare module "redis" {
         hscan(args:any[], callback?:ResCallbackT<any>): boolean;
         zscan(...args:any[]): boolean;
         zscan(args:any[], callback?:ResCallbackT<any>): boolean;
+
+        // Extras
+        duplicate(options?:any[], callback?:ResCallbackT<any>): RedisClient;
     }
 
     export interface Multi {