Fix 2018 EITC phase-out-start parameters

[martinholmer]

Revise values in policy_current_law.json to correspond to IRS published values.

[codecov[bot]]

Codecov Report

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

Project coverage is 99.42%. Comparing base (bb2c566) to head (6f9ef38).

Additional details and impacted files

[](https://app.codecov.io/gh/PSLmodels/Tax-Calculator/pull/2768?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PSLmodels) ```diff @@ Coverage Diff @@ ## master #2768 +/- ## ======================================= Coverage 99.42% 99.42% ======================================= Files 13 13 Lines 2610 2610 ======================================= Hits 2595 2595 Misses 15 15 ``` | [Flag](https://app.codecov.io/gh/PSLmodels/Tax-Calculator/pull/2768/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PSLmodels) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/PSLmodels/Tax-Calculator/pull/2768/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PSLmodels) | `99.42% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PSLmodels#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files](https://app.codecov.io/gh/PSLmodels/Tax-Calculator/pull/2768?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PSLmodels) | Coverage Δ | | |---|---|---| | [taxcalc/records.py](https://app.codecov.io/gh/PSLmodels/Tax-Calculator/pull/2768?src=pr&el=tree&filepath=taxcalc%2Frecords.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PSLmodels#diff-dGF4Y2FsYy9yZWNvcmRzLnB5) | `100.00% <ø> (ø)` | |