Add missing closing tags for li in menu template example

Also:

- "blank" -> "_blank" in target
- Re-indent whole snippet for consistency
- Do "{{ foo }}" instead of "{{foo}}" for consistency

content/templates/menu-templates.md

@@ -37,10 +37,12 @@ The following is an example:
                         {{ .Pre }}
                         <span>{{ .Name }}</span>
                     </a>
+                </li>
                 <ul class="sub-menu">
                     {{ range .Children }}
                         <li class="{{ if $currentPage.IsMenuCurrent "main" . }}active{{ end }}">
                             <a href="{{ .URL }}">{{ .Name }}</a>
+                        </li>
                     {{ end }}
                 </ul>
             {{ else }}
@@ -49,12 +51,15 @@ The following is an example:
                         {{ .Pre }}
                         <span>{{ .Name }}</span>
                     </a>
+                </li>
             {{ end }}
         {{ end }}
         <li>
-      <a href="#" target="blank">Hardcoded Link 1</a>
+            <a href="#" target="_blank">Hardcoded Link 1</a>
+        </li>
         <li>
-      <a href="#" target="blank">Hardcoded Link 2</a>
+            <a href="#" target="_blank">Hardcoded Link 2</a>
+        </li>
     </ul>
 </aside>
 {{< /code >}}