Close #3886 - Add THEAD and TBODY to scaffold markup

railties/lib/rails/generators/erb/scaffold/templates/index.html.erb

 <h1>Listing <%= plural_table_name %></h1>
 
 <table>
-  <tr>
-<% attributes.each do |attribute| -%>
-    <th><%= attribute.human_name %></th>
-<% end -%>
-    <th></th>
-    <th></th>
-    <th></th>
-  </tr>
+  <thead>
+    <tr>
+  <% attributes.each do |attribute| -%>
+      <th><%= attribute.human_name %></th>
+  <% end -%>
+      <th></th>
+      <th></th>
+      <th></th>
+    </tr>
+  </thead>
 
-  <%%= content_tag_for(:tr, @<%= plural_table_name %>) do |<%= singular_table_name %>| %>
-<% attributes.each do |attribute| -%>
-    <td><%%= <%= singular_table_name %>.<%= attribute.name %> %></td>
-<% end -%>
-    <td><%%= link_to 'Show', <%= singular_table_name %> %></td>
-    <td><%%= link_to 'Edit', edit_<%= singular_table_name %>_path(<%= singular_table_name %>) %></td>
-    <td><%%= link_to 'Destroy', <%= singular_table_name %>, confirm: 'Are you sure?', method: :delete %></td>
-  <%% end %>
+  <tbody>
+    <%%= content_tag_for(:tr, @<%= plural_table_name %>) do |<%= singular_table_name %>| %>
+  <% attributes.each do |attribute| -%>
+      <td><%%= <%= singular_table_name %>.<%= attribute.name %> %></td>
+  <% end -%>
+      <td><%%= link_to 'Show', <%= singular_table_name %> %></td>
+      <td><%%= link_to 'Edit', edit_<%= singular_table_name %>_path(<%= singular_table_name %>) %></td>
+      <td><%%= link_to 'Destroy', <%= singular_table_name %>, confirm: 'Are you sure?', method: :delete %></td>
+    <%% end %>
+  </tbody>
 </table>
 
 <br />