fix: disallow header wrapping (ietf-tools#8134)

Author: holloway

ietf/templates/base.html

@@ -46,7 +46,7 @@
                     {% endif %}
                 </a>
                 <div class="collapse navbar-collapse" id="navbar-collapse">
-                    <ul class="nav navbar-nav">
+                    <ul class="nav navbar-nav flex-nowrap">
                         {% include "base/menu.html" with flavor="top" %}
                     </ul>
                 </div>