Migrate from golang.org/x/errors

Blocked 🔴

Blocked by !20 (merged)

Overview

In !10 (merged) we started using golang.org/x/xerrors package to use the new way of how Go handles error wrapping.

The documentation about the new error wrapping can be found in https://golang.org/pkg/fmt/#Errorf and information about wrapping can be found in https://golang.org/pkg/errors/

Closes #9 (closed)