Update link to RFC 2119

Author: KorvinSzanto

spec.md

@@ -4,7 +4,7 @@ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
 "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
 interpreted as described in [RFC 2119][].
 
-[RFC 2119]: http://tools.ietf.org/html/rfc2119
+[RFC 2119]: http://datatracker.ietf.org/doc/html/rfc2119
 
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