doc: add missing `changes:` metadata for util

Ref: https://github.com/nodejs/node/pull/14558
PR-URL: https://github.com/nodejs/node/pull/14810
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

doc/api/util.md

@@ -150,6 +150,10 @@ property take precedence over `--trace-deprecation` and
 ## util.format(format[, ...args])
 <!-- YAML
 added: v0.5.3
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/14558
+    description: The `%o` and `%O` specifiers are supported now.
 -->
 
 * `format` {string} A `printf`-like format string.