Update documentation to note the new RFC.

Author: Crell

README.md

@@ -2,9 +2,9 @@
 
 [![Build Status](https://travis-ci.org/Crell/ApiProblem.svg?branch=master)](https://travis-ci.org/Crell/ApiProblem)
 
-This library provides a simple and straightforward implementation of the IETF Problem Details for HTTP APIs, [RFC 7807][1].
+This library provides a simple and straightforward implementation of the IETF Problem Details for HTTP APIs, [RFC 9457][1].
 
-[RFC 7807][1] is a simple specification for formatting error responses from RESTful APIs on the web.  This library provides a simple and convenient way to interact with that specification.  It supports generating and parsing [RFC 7807][1] messages, in both JSON and XML variants.
+[RFC 9457][1] is a simple specification for formatting error responses from RESTful APIs on the web.  This library provides a simple and convenient way to interact with that specification.  It supports generating and parsing [RFC 9457][1] messages, in both JSON and XML variants.
 
 ## Generating responses
 
@@ -102,7 +102,7 @@ This library is released under the MIT license.  In short, "leave the copyright
 
 Pull requests accepted!  The goal is complete conformance with the IETF spec.
 
-[1]: https://tools.ietf.org/html/rfc7807
+[1]: https://tools.ietf.org/html/rfc9457
 [2]: http://getcomposer.org/
 [3]: https://www.php-fig.org/psr/psr-7/
 [4]: https://www.php-fig.org/psr/psr-17/

src/ApiProblem.php

@@ -7,7 +7,7 @@
 /**
  * An API error of some form.
  *
- * This object generates errors in compliance with RFC 7807 "API Problem".
+ * This object generates errors in compliance with RFC 9457 "API Problem".
  *
  * This object should be configured via the appropriate methods, and then
  * rendered using the asJson() or asXml() methods. The resulting string is
@@ -22,7 +22,7 @@
  * to get/set those values. For extended values, use the ArrayAccess interface
  * to specify arbitrary additional properties.
  *
- * @link http://tools.ietf.org/html/rfc7807
+ * @link http://tools.ietf.org/html/rfc9457
  *
  * @author Larry Garfield
  *