Docs: correct default value of 'use_llmlingua2'

[kexplo]

What does this PR do?

The default argument for the 'use_llmlingua2' parameter is False, but the docstring is incorrectly written as True. The DOCUMENT.md file is correctly written as False.

LLMLingua/DOCUMENT.md

Line 283 in 40ac969

- **use_llmlingua2** (bool, optional): Whether to use llmlingua-2 for prompt compression. Defaults is False.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Was this discussed/approved via a Github issue? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes?
  • the document already describes it's default value is False:

    • LLMLingua/DOCUMENT.md

      Line 283 in 40ac969

      - **use_llmlingua2** (bool, optional): Whether to use llmlingua-2 for prompt compression. Defaults is False.

• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

@iofu728 @mydmdm

[iofu728]

Thanks for your help.