Proposed fix for json-ld#488

Although, as suggested in json-ld#488, an additional note would be useful, drawing the readers attention on the fact that, in this particular case, a relative IRI can *not* be used in place of an absolute IRI. I leave it to the editors to decide whether they want to include it or not.

Author: pchampin

spec/latest/json-ld/index.html

@@ -3209,7 +3209,7 @@ <h2>Node Objects</h2>
       properties of the resulting <a>node</a>.</p>
 
     <p>A <a>node object</a> MUST be a <a>JSON object</a>. All keys
-      which are not <a>IRIs</a>,
+      which are not <a>absolute IRI</a>s,
       <a>compact IRIs</a>, <a>terms</a>
       valid in the <a>active context</a>, or one of the following
       <a>keyword</a> MUST be ignored when processed:</p>