Fix text_classification example fails on Python 3 (#5590)
Fix text_classification example fails on Python 3 (#5590)

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