Fix two error on pytorch0.4 cuda

[valar000]

Fix TypeError: multinomial() missing 1 required positional arguments:"num_samples"

Fix RuntimeError: cudnn RNN backward can only be called in training mode

[zide05]

i am a newer in github, how can i down the file modified by you?

[valar000]

just clone my repositories and read git log

[zide05]

thank you!