fixed observer leak
fixed observer leak
ywzw2013/ODRefreshControl,liuzechen/ODRefreshControl,alterant-kr/ODRefreshControl,111minutes/ODRefreshControl-Fork,Sephiroth87/ODRefreshControl,zhouwude/ODRefreshControl,0xced/ODRefreshControl,lijie121210/ODRefreshControl,gank0326/waterRefresh,HelloZhu/ODRefreshControl,lyndonChen/ODRefreshControl,onetot/ODRefreshControl,cnbin/ODRefreshControl,lujianwenance/ODRefreshControl,bboyesc/ODRefreshControl,sekouperry/ODRefreshControl,hugo-/ODRefreshControl