project/
  main.go
  package1/
  package2/
  package3/

### STAGE 1: Build ###

FROM golang:1.10 as builder
WORKDIR /go/src/github.company.com/project-repo/project
COPY . .
RUN go get
RUN go install <- ERROR HERE
RUN CGO_ENABLED=0 go build -ldflags="-s -w" -o executable -a -installsuffix cgo .

### STAGE 2: Setup ###

FROM python:3.6-alpine
COPY --from=builder /go/src/github.company.com/project-repo/project/executable /api/executable
CMD ["/api/executable"]

docker build -t myapp .

main.go: cannot find package github.company.com/project-repo/project/package1 in any of:
/usr/local/go/src/github.company.com/project-repo/project/package1 (from $GOROOT)
/go/src/github.company.com/project-repo/project/package1 (from $GOPATH)