Update url and alt_url of Nathan Otterness

The previous url was the GitHub url but he has his own domain. The
alt_url is his article about the winning entry of his (of course if he
wanted something different he could do that but it's a good enough guess
for now).

author/Nathan_Otterness.json

@@ -6,8 +6,8 @@
     "sort_word" : "otterness",
     "location_code" : "US",
     "email" : "supersasquatch@gmail.com",
-    "url" : "https://github.com/yalue",
-    "alt_url" : null,
+    "url" : "https://www.nathanotterness.com",
+    "alt_url" : "https://www.nathanotterness.com/2021/04/obfuscated_c_2020.html",
     "deprecated_twitter_handle" : null,
     "mastodon" : null,
     "mastodon_url" : null,