generation_args["stop"] doesn't work for stop sequence "\n\n"

[frankxu2004]

🐛 Bug

The stop parameter provided to the API is not working as expected when stop = "\n\n"

To Reproduce

Steps to reproduce the behavior (always include the command you ran):

1. Run cmd 'metaseq-api-local'
2. Send HTTP request to /completions with parameter {"stop": "\n\n"}.
3. Still generate until max number of tokens reached.

Expected behavior

Stop after generating two consecutive newlines

Environment

• metaseq Version (master):

Additional context

When trying with other stop sequences, e.g. {"stop": "Question:"}, it works as expected.