Fix typo on 'configuration' anchor
Fix typo on 'configuration' anchor

https://rust-analyzer.github.io/manual.html#_configuration lands you at
the start of the page, while
https://rust-analyzer.github.io/manual.html#configuration correctly puts
you at the correct anchor

rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer