Update IANA contact

Change from @iherman to @pchampin.

index.html

@@ -13540,7 +13540,7 @@ <h3>Media Type Registration: `application/ld+json`</h3>
         </dl>
       </dd>
       <dt>Person &amp; email address to contact for further information:</dt>
-      <dd>Ivan Herman &lt;ivan@w3.org&gt;</dd>
+      <dd>Pierre-Antoine Champin &lt;pierre-antoine@w3.org&gt;</dd>
       <dt>Intended usage:</dt>
       <dd>Common</dd>
       <dt>Restrictions on usage:</dt>
@@ -13692,9 +13692,7 @@ <h3>Structured Suffix Registration: `+ld+json`</h3>
       information.
       -->
       <dt>Contact</dt>
-      <dd>
-        Ivan Herman &lt;[email protected]&gt;
-      </dd>
+      <dd>Pierre-Antoine Champin &lt;[email protected]&gt;</dd>
 
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