fix(ra_parser.typo): amend 'format language' to 'formal language'
//! This is the actual "grammar" of the Rust language.
//!
//! Each function in this module and its children corresponds
-//! to a production of the format grammar. Submodules roughly
+//! to a production of the formal grammar. Submodules roughly
//! correspond to different *areas* of the grammar. By convention,
//! each submodule starts with `use super::*` import and exports
//! "public" productions via `pub(super)`.
