langchain: minor changes to StuffDocumentsChain._get_inputs (#15321)

Correcting a small typo ('the' instead of 'then') and changing another
'the' (instead of 'then' too, it was a hard day for the 'n' key :D) to
'also' to match better with what is done in the code

<!-- Thank you for contributing to LangChain!

Please title your PR "<package>: <description>", where <package> is
whichever of langchain, community, core, experimental, etc. is being
modified.

Replace this entire comment with:
  - **Description:** a description of the change, 
  - **Issue:** the issue # it fixes if applicable,
  - **Dependencies:** any dependencies required for this change,
- **Twitter handle:** we announce bigger features on Twitter. If your PR
gets announced, and you'd like a mention, we'll gladly shout you out!

Please make sure your PR is passing linting and testing before
submitting. Run `make format`, `make lint` and `make test` from the root
of the package you've modified to check this locally.

See contribution guidelines for more information on how to write/run
tests, lint, etc: https://python.langchain.com/docs/contributing/

If you're adding a new integration, please include:
1. a test for the integration, preferably unit tests that do not rely on
network access,
2. an example notebook showing its use. It lives in
`docs/docs/integrations` directory.

If no one reviews your PR within a few days, please @-mention one of
@baskaryan, @eyurtsev, @hwchase17.
 -->

libs/langchain/langchain/chains/combine_documents/stuff.py

@@ -182,8 +182,8 @@ class StuffDocumentsChain(BaseCombineDocumentsChain):
     def _get_inputs(self, docs: List[Document], **kwargs: Any) -> dict:
         """Construct inputs from kwargs and docs.
 
-        Format and the join all the documents together into one input with name
-        `self.document_variable_name`. The pluck any additional variables
+        Format and then join all the documents together into one input with name
+        `self.document_variable_name`. Also pluck any additional variables
         from **kwargs.
 
         Args: