* [ios] fix bug uifont lead crash in iOS system less than 8.2 #2769
* [ios] fix bug uifont lead crash in iOS system less than 8.2 #2769

leoward/incubator-weex,leoward/incubator-weex,alibaba/weex,dianwodaMobile/DWeex,Hanks10100/incubator-weex,erha19/incubator-weex,MrRaindrop/incubator-weex,Hanks10100/incubator-weex,weexteam/incubator-weex,MrRaindrop/incubator-weex,acton393/incubator-weex,xiayun200825/weex,Hanks10100/incubator-weex,alibaba/weex,alibaba/weex,acton393/incubator-weex,Neeeo/incubator-weex,alibaba/weex,cxfeng1/incubator-weex,erha19/incubator-weex,miomin/incubator-weex,cxfeng1/incubator-weex,yuguitao/incubator-weex,miomin/incubator-weex,MrRaindrop/incubator-weex,Neeeo/incubator-weex,alibaba/weex,KalicyZhou/incubator-weex,cxfeng1/incubator-weex,yuguitao/incubator-weex,erha19/incubator-weex,yuguitao/incubator-weex,xiayun200825/weex,miomin/incubator-weex,yuguitao/incubator-weex,erha19/incubator-weex,weexteam/incubator-weex,erha19/incubator-weex,MrRaindrop/incubator-weex,leoward/incubator-weex,KalicyZhou/incubator-weex,erha19/incubator-weex,dianwodaMobile/DWeex,xiayun200825/weex,acton393/incubator-weex,leoward/incubator-weex,dianwodaMobile/DWeex,leoward/incubator-weex,Hanks10100/incubator-weex,Neeeo/incubator-weex,Hanks10100/incubator-weex,acton393/incubator-weex,yuguitao/incubator-weex,weexteam/incubator-weex,weexteam/incubator-weex,xiayun200825/weex,acton393/incubator-weex,dianwodaMobile/DWeex,KalicyZhou/incubator-weex,MrRaindrop/incubator-weex,MrRaindrop/incubator-weex,miomin/incubator-weex,cxfeng1/incubator-weex,acton393/incubator-weex,Neeeo/incubator-weex,weexteam/incubator-weex,KalicyZhou/incubator-weex,cxfeng1/incubator-weex,leoward/incubator-weex,alibaba/weex,miomin/incubator-weex,miomin/incubator-weex,cxfeng1/incubator-weex,miomin/incubator-weex,KalicyZhou/incubator-weex,yuguitao/incubator-weex,Hanks10100/incubator-weex,erha19/incubator-weex,acton393/incubator-weex,dianwodaMobile/DWeex,Neeeo/incubator-weex,weexteam/incubator-weex,miomin/incubator-weex,alibaba/weex,dianwodaMobile/DWeex,xiayun200825/weex,xiayun200825/weex,Neeeo/incubator-weex,acton393/incubator-weex,KalicyZhou/incubator-weex,erha19/incubator-weex,Hanks10100/incubator-weex,Hanks10100/incubator-weex