Update rustfmt to 0.9.0, racer to 2.1.2 and rls-vfs to 0.4.6.

We need to update rustc-ap-syntax to 209 to unblock nightly.

In rustfmt 0.9.0, the `format_input` function has been replaced by the
`Session` struct. The `reformat` function is thus modified for the new API.

Author: kennytm