Update spec/index.html

Co-authored-by: Ted Thibodeau Jr <[email protected]>

Author: afs

spec/index.html

@@ -10460,7 +10460,7 @@ <h3>Grammar</h3>
           <li>A <a href="#rReifier">reifier</a> or
             <a href="#rAnnotationBlockPath">annotation syntax</a>
             is only permitted after a triple when the property position is
-            a simple path (IRI, the keyword <code>a</code> or a variable),
+            a simple path (an IRI, the keyword <code>a</code>, or a variable),
             and not for other path expressions.
           </li>
         </ol>