Convert from go-git to git2go

vendor/gopkg.in/src-d/go-git.v4/utils/diff/diff.go

vendor/gopkg.in/src-d/go-git.v4/utils/ioutil/common.go

vendor/gopkg.in/src-d/go-git.v4/utils/merkletrie/change.go

vendor/gopkg.in/src-d/go-git.v4/utils/merkletrie/difftree.go

vendor/gopkg.in/src-d/go-git.v4/utils/merkletrie/doc.go

...r/gopkg.in/src-d/go-git.v4/utils/merkletrie/doubleiter.go

.../src-d/go-git.v4/utils/merkletrie/internal/frame/frame.go

vendor/gopkg.in/src-d/go-git.v4/utils/merkletrie/iter.go

.../gopkg.in/src-d/go-git.v4/utils/merkletrie/noder/noder.go

...r/gopkg.in/src-d/go-git.v4/utils/merkletrie/noder/path.go

vendor/gopkg.in/src-d/go-git.v4/worktree.go

vendor/gopkg.in/src-d/go-git.v4/worktree_darwin.go

vendor/gopkg.in/src-d/go-git.v4/worktree_linux.go

vendor/gopkg.in/warnings.v0/LICENSE

vendor/gopkg.in/warnings.v0/README

vendor/gopkg.in/warnings.v0/warnings.go

vendor/vendor.json