DBN implementation may cause gpu memory leaks.

[Tangshitao]

I tried to run DBN, but the implementation cause gpu memory leaks in my computer whose torch version is 0.4.1. I fix this by changing the following lines of codes
self.running_mean = (1. - self.momentum) * self.running_mean + self.momentum * mean
self.running_projection = (1. - self.momentum) * self.running_projection + self.momentum * wm
to
self.running_mean = (1. - self.momentum) * self.running_mean + self.momentum * mean.data
self.running_projection = (1. - self.momentum) * self.running_projection + self.momentum * wm.data