fix message

lib/views/crowi-plus/new_page.html

@@ -38,7 +38,7 @@
         {% block content_main_before %}
         <h2 class="text-muted">
           <i class="fa fa-info-circle" aria-hidden="true"></i>
-          Page is not exists
+          Page is not found
         </h2>
         {% endblock %}