Rollup merge of rust-lang#64961 - rust-lang:spastorino-patch-1, r=oli-obk

Make comment about dummy type a bit more clear

Author: Centril

src/librustc/ty/mod.rs

@@ -600,7 +600,8 @@ impl<'tcx> rustc_serialize::UseSpecializedDecodable for Ty<'tcx> {}
 pub type CanonicalTy<'tcx> = Canonical<'tcx, Ty<'tcx>>;
 
 extern {
-    /// A dummy type used to force `List` to by unsized without requiring fat pointers.
+    /// A dummy type used to force `List` to be unsized while not requiring references to it be wide
+    /// pointers.
     type OpaqueListContents;
 }