Add #![forbid(unsafe_code)] crate attribute
Add #![forbid(unsafe_code)] crate attribute

Pretty sure that unsafe code is never going to be a problem with this
crate, but it can help a bit when inspecting the `cargo-geiger` output
of a dependency tree, and having it in the `lib.rs` gives off a warm,
fuzzy feeling.

gluon-lang/languageserver-types