Change default dtype from fp64 to fp32
Change default dtype from fp64 to fp32

chainer/chainer,wkentaro/chainer,chainer/chainer,okuta/chainer,okuta/chainer,hvy/chainer,chainer/chainer,niboshi/chainer,okuta/chainer,wkentaro/chainer,niboshi/chainer,hvy/chainer,okuta/chainer,hvy/chainer,chainer/chainer,niboshi/chainer,wkentaro/chainer,wkentaro/chainer,pfnet/chainer,niboshi/chainer,hvy/chainer