Update go-git to github.com/go-git/go-git

[matthewmcnew]

• gopkg.in/src-d/go-git is no longer being updated and the project has moved to github.com/go-git/go-git

[codecov-commenter]

Codecov Report

Merging #421 into master will increase coverage by 0.20%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #421      +/-   ##
==========================================
+ Coverage   67.08%   67.29%   +0.20%     
==========================================
  Files          85       85              
  Lines        3625     3611      -14     
==========================================
- Hits         2432     2430       -2     
+ Misses        907      895      -12     
  Partials      286      286              

Impacted Files	Coverage Δ
pkg/git/fetch.go	60.41% <ø> (ø)
pkg/git/git_keychain.go	80.32% <ø> (ø)
pkg/git/k8s_git_keychain.go	89.47% <ø> (ø)
pkg/git/remote_git_resolver.go	95.34% <ø> (ø)
pkg/apis/build/v1alpha1/source_resolver.go	0.00% <0.00%> (-6.07%)	⬇️
...erimental/v1alpha1/custom_cluster_builder_types.go	0.00% <0.00%> (ø)

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