fixed download_articles method to support multithreading
fixed download_articles method to support multithreading

curita/newspaper,autumnz613/HangzhoulLianjia,tarundeep30000/newspaper,curita/newspaper,muntasir2000/newspaper,cantino/newspaper,tarundeep30000/newspaper,surajssd/newspaper,kotrfa/newspaper,elaatifi/newspaper,cantino/newspaper,ChiragChhatbar/newspaper,ThoughtWorksInc/newspaper,itech001/newspaper,ChiragChhatbar/newspaper,davecrumbacher/newspaper,Tskatom/newspaper,wannaphongcom/newspaper,shagunsodhani/newspaper,Factr/newspaper,MathematicianVogt/newspaper