Fix typo Update model_assumptions

[bravesasha]

There is a typo in the documentation

Fix #Issue

Changes proposed in this pull request:

• Your_changes

The following steps were realized, as well (required):

• Update the CHANGELOG.md
• Check if full simulation tests pass locally (EXECUTE_TESTS_ON=master pytest)

Also the following steps were realized (if applies):

• Use in-line comments to explain your code
• Write docstrings to your code
• For new functionalities: Explain in readthedocs
• Write test(s) for your new patch of code

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• Done

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