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

[review-notebook-app]

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Codecov Report

All modified and coverable lines are covered by tests ✅

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

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Additional details and impacted files

@@                 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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