project
- main.go
- internal
  - utils.go
- go.mod (github.internal.com/team_name/project_name)
- vendor
  - go.uber.org
  - private.repo.com
Dockerfile

import (
    "github.internal.com/team_name/project_name/internal"
    "go.uber.org/zap"
)

ENV GOPATH /go
COPY . /go/src/github.internal.com/team_name/project_name
WORKDIR /go/src/github.internal.com/team_name/project_name
RUN CGO_ENABLED=0 GOOS=linux go build -a -o slaxtract main.go

main.go:7:2: cannot find package "github.internal.com/team_name/project_name/internal" in any of:
    /usr/local/go/src/github.internal.com/team_name/project_name/internal (from $GOROOT)
    /go/src/github.internal.com/team_name/project_name/internal (from $GOPATH)