billing: Fix missing target=blank for new navbar menu items.

Author: timabbott

templates/zerver/app/navbar.html

@@ -157,14 +157,14 @@
                             {% endif %}
                             {% if show_plans %}
                             <li role="presentation">
-                                <a href="/plans" role="menuitem">
+                                <a href="/plans" target="_blank" role="menuitem">
                                     <i class="fa fa-rocket" aria-hidden="true"></i> {{ _('Plans and pricing') }}
                                 </a>
                             </li>
                             {% endif %}
                             {% if show_billing %}
                             <li role="presentation">
-                                <a href="/billing" role="menuitem">
+                                <a href="/billing" target="_blank" role="menuitem">
                                     <i class="fa fa-credit-card" aria-hidden="true"></i> {{ _('Billing') }}
                                 </a>
                             </li>