Update functional/stateful-types.md

Author: simonsan

functional/stateful-types.md

@@ -243,6 +243,6 @@ There are a number of simpler state machines, however, that have their own patte
 
 ## See also
 
-* [The Case for the Type State Pattern](https://www.novatec-gmbh.de/en/blog/the-case-for-the-typestate-pattern-the-typestate-pattern-itself/)
+* [The Case for the Type State Pattern](https://web.archive.org/web/20210325065112/https://www.novatec-gmbh.de/en/blog/the-case-for-the-typestate-pattern-the-typestate-pattern-itself/)
 * FIXME: I remember seeing a Rust talk which described this in more detail, but I
 can't find it again.