Update minimessage format docs link

[rymiel]

As per KyoriPowered/adventure-docs#45, the documentation for minimessage was split up into two pages and no longer uses a fragment in the link. While old links still continue to work, they don't directly bring the user directly to the format page as before

[YouHaveTrouble]

you just removed .html from the url, the actual link to the same page is now https://docs.adventure.kyori.net/minimessage/format