Target java 8

[RustedBones]

compiled java classes are not java 8 compatible

[codecov]

Codecov Report

Merging #608 (e39eb66) into main (62a5fe3) will decrease coverage by 0.00%.
The diff coverage is n/a.

❗ Current head e39eb66 differs from pull request most recent head a1e5a72. Consider uploading reports for the commit a1e5a72 to get more accurate results

@@            Coverage Diff             @@
##             main     #608      +/-   ##
==========================================
- Coverage   96.11%   96.11%   -0.01%     
==========================================
  Files          49       48       -1     
  Lines        1649     1648       -1     
  Branches      152      152              
==========================================
- Hits         1585     1584       -1     
  Misses         64       64              

Impacted Files	Coverage Δ
.../src/main/scala-2.13/magnolify/shims/package.scala

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[mattnworb]

should fix #609