wrap LSTMCell in DropoutWrapper if dropout param
wrap LSTMCell in DropoutWrapper if dropout param

Adds a `dropout=_` param to `lstm()`, which if provided wraps `lstm_cell` in a `rnn.DropoutWrapper` for regularization. Feel free to close if there's a smarter way, more for consideration on providing a dropout option for these layers where applicable.

lefnire/tensorforce,reinforceio/tensorforce