Fix typo

Author: taiki-e

src/lib.rs

@@ -1206,7 +1206,7 @@ macro_rules! __pin_project_make_unpin_impl {
         // this would cause an E0446 (private type in public interface).
         //
         // When RFC 2145 is implemented (rust-lang/rust#48054),
-        // this will become a lint, rather then a hard error.
+        // this will become a lint, rather than a hard error.
         //
         // As a workaround for this, we generate a new struct, containing all of the pinned
         // fields from our #[pin_project] type. This struct is declared within