update docstring in roi_average_align_2d
update docstring in roi_average_align_2d

okuta/chainer,pfnet/chainer,chainer/chainer,wkentaro/chainer,okuta/chainer,tkerola/chainer,ktnyt/chainer,niboshi/chainer,keisuke-umezawa/chainer,chainer/chainer,niboshi/chainer,chainer/chainer,jnishi/chainer,wkentaro/chainer,hvy/chainer,chainer/chainer,ktnyt/chainer,niboshi/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,ktnyt/chainer,hvy/chainer,hvy/chainer,jnishi/chainer,jnishi/chainer,wkentaro/chainer,niboshi/chainer,hvy/chainer,wkentaro/chainer,okuta/chainer,ktnyt/chainer,keisuke-umezawa/chainer,jnishi/chainer,okuta/chainer