Fix insert method of Sequential
Fix insert method of Sequential

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