message: Correct phrasing on CuDNN conditions
  As-is, the condition means "inputs are not masked" AND "inputs are not strictly right-padded", which isn't the actual condition, and is thereby misleading.
diff: @@ -204,7 +204,7 @@ class GRU(recurrent.DropoutRNNCellMixin, recurrent.GRU):
  4. `unroll` is `False`
  5. `use_bias` is `True`
  6. `reset_after` is `True`
  - 7. Inputs are not masked or strictly right padded.
  + 7. Inputs, if use masking, are strictly right-padded.
  There are two variants of the GRU implementation. The default one is based on
  [v3](https://arxiv.org/abs/1406.1078v3) and has reset gate applied to hidden
  @@ -933,7 +933,7 @@ class LSTM(recurrent.DropoutRNNCellMixin, recurrent.LSTM):
  3. `recurrent_dropout` == 0
  4. `unroll` is `False`
  5. `use_bias` is `True`
  - 6. Inputs are not masked or strictly right padded.
  + 6. Inputs, if use masking, are strictly right-padded.
  For example:
  