update go-git v4 api

[smola]

No description provided.

[codecov-io]

Codecov Report

Merging #119 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #119   +/-   ##
=======================================
  Coverage   85.23%   85.23%           
=======================================
  Files          11       11           
  Lines         325      325           
=======================================
  Hits          277      277           
  Misses         42       42           
  Partials        6        6

Impacted Files	Coverage Δ
tree_entries.go	83.33% <ø> (ø)	✅
blobs.go	77.14% <ø> (ø)	✅
tags.go	82.22% <ø> (ø)	✅
objects.go	77.14% <ø> (ø)	✅
commits.go	82.97% <ø> (ø)	✅
references.go	82.22% <ø> (ø)	✅
database.go	100% <ø> (ø)	✅

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