Update RLS

This update includes the ability to warn on deprecated config keys.
It's important to be able to warn the user whenever they're using
an old configuration rather than giving them a cryptic "unknown
configuration error"

cc rust-lang/vscode-rust#639

Since we removed a config value in the current nightly, it'd be
very good if this change can make also make it before cutting the
next release.

Author: Xanewok