Fix a typo in tokenizer documentation

[mssalvatore]

What does this PR do?

Fixes a typo in tokenizer documentation. For some methods, such as tokenize(), the description currently reads "Converts a string in a sequence of tokens, using the tokenizer." I believe what is meant is "Converts a string INTO a sequence of tokens".

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
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• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests? (N/A)

Who can review?

@ArthurZucker
@sgugger

[ArthurZucker]

Thanks 🤗

[HuggingFaceDocBuilderDev]

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