nerdm-intro-body.html: fix value type glossary def link

etc/help/nerdm-intro-body.html

@@ -50,7 +50,7 @@ <h3>What a NERDm record looks like</h3>
 resource.  The metadata is in the form of a set of <em>properties</em>.  A
 <a href="#def:property" title="definition: property">property</a> is a
 piece of metadata that has a <em>name</em> and a <em>value</em>.  The
-<a href="def:value_type" title="definition: value type">value</a> can
+<a href="def:type" title="definition: value type">value</a> can
 be a single value (e.g. text, a number, true/false), a list of values,
 or a complex values made up of sub-properties.  
 </p>