Fix typo in verification method definition.

Co-authored-by: Ted Thibodeau Jr <tthibodeau@openlinksw.com>

index.html

@@ -618,7 +618,7 @@ <h3>Terminology</h3>
           <dt><dfn class="export">verification method</dfn></dt>
           <dd>
             <p>
-A method and its parameters used to independently verify a proof. For
+A method and its parameters, used to independently verify a proof. For
 example, a cryptographic public key can be used as a verification method with
 respect to a digital signature; in such use, it verifies that the signer
 used the associated cryptographic private key.