Fix grammar in zero_authorized_projects view

app/views/dashboard/_zero_authorized_projects.html.haml

@@ -29,7 +29,7 @@
       %p.slead
         You can create a group for several dependent projects.
         %br
-        Group is the best way to manage projects and members
+        Groups are the best way to manage projects and members
       .link_holder
         = link_to new_group_path, class: "btn btn-new" do
           New group »