ra_hir: fix typo
//!
//! `ra_hir_*` crates are the implementation of the compiler logic.
//! They are written in "ECS" style, with relatively little abstractions.
-//! Many types are not self-contained, and explicitelly use local indexes, arenas, etc.
+//! Many types are not self-contained, and explicitly use local indexes, arenas, etc.
//!
//! `ra_hir` is what insulates the "we don't know how to actually write an incremental compiler"
//! from the ide with completions, hovers, etc. It is a (soft, internal) boundary:
