Update spec/index.html

Co-authored-by: Gregg Kellogg <[email protected]>

Author: afs

spec/index.html

@@ -786,7 +786,7 @@ <h2>Literals and datatypes</h2>
     or <a data-cite="RDF12-CONCEPTS#dfn-directional-language-tagged-string"><code>rdf:dirLangString</code></a>
     as their datatype are given special treatment.
     The IRIs <code>rdf:langString</code> and <code>rdf:dirLangString</code>
-    are classified as a datatype IRIs and interpreted to denote a datatype,
+    are classified as datatype IRIs and interpreted to denote a datatype,
     even though no <a>L2V</a> mapping is defined for them.
     The <a>value space</a> of <code>rdf:langString</code>
     is the set of all pairs of a string with a language tag.