Update external URLs failing in build

docs/testing/ponycheck.md

@@ -61,7 +61,7 @@ class _ListReverseOneProperty is Property1[Array[USize]]
 
 ## Integration with PonyTest
 
-PonyCheck properties need to be executed. The test runner for PonyCheck is [PonyTest](https://stdlib.ponylang.io/pony_test--index). To integrate [`Property1`](https://stdlib.ponylang.io/pony_check-Property1) into [PonyTest](https://stdlib.ponylang.io/pony_test--index), `Property1` needs to be wrapped inside a [`Property1UnitTest`](hhttps://stdlib.ponylang.io/pony_check-Property1UnitTest) and passed to the PonyTest `apply` method as a regular PonyTest [`UnitTest`](https://stdlib.ponylang.io/pony_test-UnitTest):
+PonyCheck properties need to be executed. The test runner for PonyCheck is [PonyTest](https://stdlib.ponylang.io/pony_test--index). To integrate [`Property1`](https://stdlib.ponylang.io/pony_check-Property1) into [PonyTest](https://stdlib.ponylang.io/pony_test--index), `Property1` needs to be wrapped inside a [`Property1UnitTest`](https://stdlib.ponylang.io/pony_check-Property1UnitTest) and passed to the PonyTest `apply` method as a regular PonyTest [`UnitTest`](https://stdlib.ponylang.io/pony_test-UnitTest):
 
 ```pony
 use "pony_test"

docs/types/at-a-glance.md

@@ -31,7 +31,7 @@ The Pony type system offers a lot of guarantees, even more than other statically
 * Your program will never deadlock.
 * Your code will always be capabilities-secure.
 * All message passing is
-[causal](https://courses.cs.vt.edu/~cs5204/fall00/causal.html). (Not **casual**!)
+[causal](https://web.archive.org/web/20221206095540/https://courses.cs.vt.edu/~cs5204/fall00/causal.html). (Not **casual**!)
 
 Some of those will make sense right now. Some of them may not mean much to you yet (like capabilities-security and causal messaging), but we'll get to those concepts later on.