update_client: Replace base::MakeUnique with std::make_unique

Bug: 755727
Change-Id: I51a9cfe9d116cded27e81142851fda3f9c054b8e
Reviewed-on: https://chromium-review.googlesource.com/846604
Reviewed-by: Sorin Jianu <[email protected]>
Commit-Queue: Jinho Bang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#527329}
12 files changed