turn the multi-trigger condition off by default (#1306)

MJRefresh/Base/MJRefreshAutoFooter.m

@@ -57,7 +57,7 @@ - (void)prepare
     self.automaticallyRefresh = YES;
     
     // 默认是当offset达到条件就发送请求（可连续）
-    self.onlyRefreshPerDrag = NO;
+    self.onlyRefreshPerDrag = YES;
 }
 
 - (void)scrollViewContentSizeDidChange:(NSDictionary *)change