Updates for PowerModels v0.20 and Julia v1.6

[codecov[bot]]

Codecov Report

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

Comparison is base (2c48fa8) 90.41% compared to head (9861835) 89.13%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #70 +/- ## ========================================== - Coverage 90.41% 89.13% -1.28% ========================================== Files 25 25 Lines 2169 2154 -15 ========================================== - Hits 1961 1920 -41 - Misses 208 234 +26 ```

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