Editorial: fix minor copypasta: s/superscript/subscript/ (#2393)

Just a minor editorial/typo change to fix some copypasta.

index.html

@@ -8309,7 +8309,7 @@ <h5>Presentational Role Inheritance</h5>
 		<div class="role" id="superscript">
 			<rdef>superscript</rdef>
 			<div class="role-description">
-				<p>One or more superscripted characters.  See related <rref>superscript</rref>.</p>
+				<p>One or more superscripted characters.  See related <rref>subscript</rref>.</p>
 				<p>The <code>superscript</code> role is intended to be used only to mark up typographical conventions that have specific meanings; not for typographical presentation for presentation's sake. In general, authors SHOULD use this role only if the absence of the superscript would change the meaning of the content.</p>
 			</div>
 			<table class="role-features">