Use type hint in communicator_base.py
Use type hint in communicator_base.py

niboshi/chainer,chainer/chainer,chainer/chainer,niboshi/chainer,pfnet/chainer,hvy/chainer,niboshi/chainer,hvy/chainer,chainer/chainer,hvy/chainer,niboshi/chainer,chainer/chainer,hvy/chainer