Update `_process_sequence()` docstring

[rogerioagjr]

Small modification in the documentation of _process_sequence to reflect the correct order (hidden_state, cell_state) of lstm_states.

See order here: https://pytorch.org/docs/stable/generated/torch.nn.LSTM.html

Description

Context

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Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Documentation (update in the documentation)

Checklist:

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• [ ] The functionality/performance matches that of the source (required for new training algorithms or training-related features).
• [ ] I have updated the tests accordingly (required for a bug fix or a new feature).
• [ ] I have included an example of using the feature (required for new features).
• [ ] I have included baseline results (required for new training algorithms or training-related features).
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