Fix orchestrator/go.sum

What does this MR do?

Fixes mismatched checksum for github.com/docker/docker v0.7.3-0.20181024032540-785fe99bdb7c in orchestrator/go.sum.

This MR results from changes after sed -e '#github.com/docker/docker#d' orchestrator/go.sum; cd orchestrator; go get.

What are the relevant issue numbers?

gitlab-org/gitlab#211446 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• [n/a] Documentation created/updated for GitLab EE, if necessary
• [n/a] Documentation created/updated for this project, if necessary
• [n/a] Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• [n/a] Job definition updated, if necessary
  • [n/a] Auto-DevOps template
  • [n/a] Job definition example
  • [n/a] CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• [n/a] Security reports checked/validated by reviewer

cf. !15 (merged)