Update index.html

Co-authored-by: Orie Steele <orie@or13.io>

Author: marcoscaceres

index.html

@@ -401,7 +401,7 @@ <h2 id="protocol-registry">
       Registry of protocols for requesting digital credential
     </h2>
     <p>
-      The following is the <dfn data-lt="digital credentials registry">digital
+      The following are <dfn data-lt="digital credentials registry">digital
       credentials registryls exchange protocols</dfn> that are supported by
       this specification.
     </p>