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

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