Fixes example signature name typo

The example contains Ed25519 signature instead of RSA as mentioned
in the line.

Author: kushaldas

index.html

@@ -1736,7 +1736,7 @@ <h3>Proofs (Signatures)</h3>
 For example, if digital signatures are used for the proof mechanism, the
 <code>proof</code> <a>property</a> is expected to have name-value pairs that
 include a signature, a reference to the signing entity, and a representation of
-the signing date. The example below uses RSA digital signatures.
+the signing date. The example below uses Ed25519 digital signatures.
         </p>
 
         <pre class="example nohighlight"