feat: support esm

[yeonjuan]

fixes #15

[codecov-commenter]

Codecov Report

Merging #16 (9914159) into main (5d6d193) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #16   +/-   ##
=======================================
  Coverage   98.10%   98.10%           
=======================================
  Files           4        4           
  Lines         158      158           
  Branches       38       36    -2     
=======================================
  Hits          155      155           
  Misses          2        2           
  Partials        1        1           

Flag	Coverage Δ
unittest	98.10% <100.00%> (ø)

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Impacted Files	Coverage Δ
src/parse-git-diff.ts	97.82% <100.00%> (ø)