Update spec/index.html

Co-authored-by: Olaf Hartig <[email protected]>

Author: afs

spec/index.html

@@ -6532,7 +6532,7 @@ <h5>STRDT</h5>
             <p>The <code>STRDT</code> function constructs a literal with
               <a data-cite="RDF12-CONCEPTS#dfn-lexical-form">lexical form</a>
               and 
-              <a data-cite="RDF12-CONCEPTS#dfn-datatype">datatype</a>
+              <a data-cite="RDF12-CONCEPTS#dfn-datatype-iri">datatype IRI</a>
               as specified by the arguments.
             </p>
             <div class="result">