Fix contiguous output bug in nn.Mean
Fix contiguous output bug in nn.Mean

caldweln/nn,douwekiela/nn,jhjin/nn,sbodenstein/nn,GregSatre/nn,davidBelanger/nn,EnjoyHacking/nn,jzbontar/nn,ivendrov/nn,Jeffyrao/nn,xianjiec/nn,eulerreich/nn,Djabbz/nn,PraveerSINGH/nn,eriche2016/nn,ominux/nn,PierrotLC/nn,joeyhng/nn,colesbury/nn,lukasc-ch/nn,abeschneider/nn,nicholas-leonard/nn,diz-vara/nn,noa/nn,forty-2/nn,zhangxiangxiao/nn,rotmanmi/nn,witgo/nn,andreaskoepf/nn,kmul00/nn,mlosch/nn,apaszke/nn,sagarwaghmare69/nn,elbamos/nn,LinusU/nn,adamlerer/nn,bartvm/nn,Moodstocks/nn,lvdmaaten/nn,Aysegul/nn,vgire/nn,clementfarabet/nn,jonathantompson/nn