Update Go builder to latest version of library

[ianlewis]

Related #67

[ianlewis]

@laurentsimon We should probably discuss whether it's worth it to continue to have a separate go.mod for the Go builder. I think we addressed privacy by adding it to internal and I'm doubtful the Go builder will have significantly more dependencies than the base library, but I'd like your thoughts.

In the future, I can definitely see us having a separate go.mod for a Docker builder (e.g. #23). For example, if we need to import Docker client that would import a huge number of transient dependencies.

[laurentsimon]

Let's merge the go.mod, there does not seem to be a simple solution to this at the moment. We can re-visit later if this becomes an issue.
Thanks @ianlewis and @asraa for bringing this up

[laurentsimon]

I needed this as part of #142, so I made the changes in the PR