Update spec/index.html

Co-authored-by: Dan Yamamoto <yamdan@gmail.com>

Author: gkellogg

spec/index.html

@@ -292,7 +292,7 @@ <h2>A Canonical form of N-Quads</h2>
     <p>A future version may consider requiring all characters between
       `U+0000` and `U+001F` (other than `U+000A` (<code title="LINE FEED"><sub>LF</sub></code>)
       and `U+000D` (<code title="CARRIAGE RETURN"><sub>CR</sub></code>))
-      along with `U+007F` <code title="delete">DEL</code>
+      along with `U+007F` (<code title="delete"><sub>DEL</sub></code>)
       to be represented using `UCHAR`.</p>
   </div>
 </section>