Copy header Link for canonical image SEO

[xavren]

Cf https://www.maxcdn.com/blog/better-image-seo-canonical-headers/

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

---

• If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data and verify that your email is set on your git commits.
• If you signed the CLA as a corporation, please let us know the company's name.

[willnorris]

remove trailing space on this line. (or just run gofmt which will do this for you)

[googlebot]

CLAs look good, thanks!

[xavren]

i will do a clean rebase

[willnorris]

you don't need to close this PR to do a clean rebase. Just rebase your branch and force push to GitHub.

[xavren]

You're right, here you go