go-diff dependency

[godofdream]

1. Version of golangci-lint: golangci-lint --version (or git commit if you don't use binary distribution)
   de1d1ad

sourcegraph.com/sourcegraph/go-diff@v0.5.1 moved to github.com/sourcegraph/go-diff/diff
This needs to be updated

[godofdream]

#487

[jirfag]

thank you, closing as #487 was merged