allow "rows" attrib of coderesponse textbox to set box height

common/lib/capa/capa/templates/codeinput.html

@@ -50,6 +50,7 @@
         },
         smartIndent: false
       });
+      $("#textbox_${id}").find('.CodeMirror-scroll').height(${int(13.5*eval(rows))});
     });
   </script>
 </section>