Update metadata.toml (#2487)

Broken link was causing CI checks to fail.

Author: Cool-Katt

exercises/pov/metadata.toml

@@ -1,4 +1,4 @@
 title = "POV"
 blurb = "Reparent a graph on a selected node."
 source = "Adaptation of exercise from 4clojure"
-source_url = "https://www.4clojure.com/"
+source_url = "https://github.com/oxalorg/4ever-clojure"