Fix minor typos for ItemLocalId

* added comma before 'that is'
* "can be implement" -> "can be implemented"

Author: shiatsumat

src/librustc/hir/mod.rs

@@ -126,12 +126,12 @@ mod item_local_id_inner {
     use rustc_macros::HashStable;
     newtype_index! {
         /// An `ItemLocalId` uniquely identifies something within a given "item-like",
-        /// that is within a hir::Item, hir::TraitItem, or hir::ImplItem. There is no
+        /// that is, within a hir::Item, hir::TraitItem, or hir::ImplItem. There is no
         /// guarantee that the numerical value of a given `ItemLocalId` corresponds to
         /// the node's position within the owning item in any way, but there is a
         /// guarantee that the `LocalItemId`s within an owner occupy a dense range of
         /// integers starting at zero, so a mapping that maps all or most nodes within
-        /// an "item-like" to something else can be implement by a `Vec` instead of a
+        /// an "item-like" to something else can be implemented by a `Vec` instead of a
         /// tree or hash map.
         pub struct ItemLocalId {
             derive [HashStable]