Update chainer/optimizers/adam.py
Update chainer/optimizers/adam.py

Co-Authored-By: hitsgub <e131c83cac67b8b9c0b08c9a453f1229fb04ecc9@gmail.com>
chainer/chainer,keisuke-umezawa/chainer,chainer/chainer,okuta/chainer,chainer/chainer,niboshi/chainer,keisuke-umezawa/chainer,wkentaro/chainer,okuta/chainer,niboshi/chainer,okuta/chainer,wkentaro/chainer,niboshi/chainer,niboshi/chainer,tkerola/chainer,hvy/chainer,okuta/chainer,hvy/chainer,wkentaro/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,hvy/chainer,wkentaro/chainer,hvy/chainer,pfnet/chainer,chainer/chainer