Notebook linting errors fix

[Chase-Grajeda]

Added newline to end of breaking notebooks:

• Covid19_Initial_Posterior_Estimation.ipynb
• LCA_Model_Posterior_Estimation.ipynb
• Model_Comparison_MPT.ipynb

Linter is still failing due to unfinished changes in base_approximator.py, which is out of scope for this fix

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 66.32%. Comparing base (e829619) to head (2267771).

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## streamlined-backend #177 +/- ## ==================================================== Coverage 66.32% 66.32% ==================================================== Files 91 91 Lines 1675 1675 ==================================================== Hits 1111 1111 Misses 564 564 ```

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