Fix link in Any documentation

[jnicklas]

The link in the documentation for std::any::Any linking to the module level documentation was mistakenly leading to std instead of std::any.

r? @steveklabnik

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @steveklabnik (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see CONTRIBUTING.md for more information.

[steveklabnik]

I just accepted another PR with this change: #24113 Thanks though!