Update: Add rel=sponsored to sponsor links (#780)
Update: Add rel=sponsored to sponsor links (#780)

This should help further qualify these links to search engines. I found
documentation that Google and Bing both support the attribute and treat
it the same as `nofollow`, but I left `nofollow` as a fallback for any
others that might not.

https://support.google.com/webmasters/answer/96569?hl=en
eslint/cn.eslint.org