docs: fix missing closing comment

Signed-off-by: Athan <kgryte@gmail.com>

Author: kgryte

lib/node_modules/@stdlib/blas/ext/base/ndarray/gnansumkbn2/README.md

@@ -102,6 +102,8 @@ console.log( v );
 
 </section>
 
+<!-- /.references -->
+
 <!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
 
 <section class="related">