Use www.rfc-editor.org for RFC text.

We use the following site for that now:

* https://tools.ietf.org/ or http
* https://datatracker.ietf.org or http

Today, IETF said the official site of RFC is www.rfc-editor.org.

FYI: https://authors.ietf.org/en/references-in-rfcxml

I replaced them to www.rfc-editor.org.

lib/random/formatter.rb

@@ -165,7 +165,7 @@ def urlsafe_base64(n=nil, padding=false)
   #
   # The result contains 122 random bits (15.25 random bytes).
   #
-  # See RFC4122[https://datatracker.ietf.org/doc/html/rfc4122] for details of UUID.
+  # See RFC4122[https://www.rfc-editor.org/rfc/rfc4122] for details of UUID.
   #
   def uuid
     ary = random_bytes(16)