fix redisscheduler #583

webmagic-extension/src/main/java/us/codecraft/webmagic/scheduler/RedisScheduler.java

@@ -48,7 +48,7 @@ public class RedisScheduler extends DuplicateRemovedScheduler implements Monitor
     public boolean isDuplicate(Request request, Task task) {
         Jedis jedis = pool.getResource();
         try {
-            return jedis.sadd(getSetKey(task), request.getUrl()) > 0;
+            return jedis.sadd(getSetKey(task), request.getUrl()) == 0;
         } finally {
             pool.returnResource(jedis);
         }