Clean Go source code

[micheartin]

Used golangci-lint and fixed some linter warnings.

docker run --rm --user $(id -u) \
    -v $(pwd):/app -w /app      \
    -v ~/.cache:/.cache         \
    golangci/golangci-lint golangci-lint run --enable-all ./...

[pkieltyka]

I prefer not these kinds of auto-PRs, thanks tho

[micheartin]

All right. I have created a fork with these changes and other experimental contributions found on others docgen repositories.
https://github.com/micheartin/docgen
https://github.com/go-chi/docgen/network
Let me know if you want a partial PR of this fork.