Ensure that sign-in link is center-justified

Author: rsmithlal

app/views/layouts/better_together/_header.html.erb

@@ -71,7 +71,7 @@
                   </span>
                 <% end %>
               <% else %>
-                <%= link_to new_user_session_path, class: "nav-link d-flex align-items-center gap-2" do %>
+                <%= link_to new_user_session_path, class: "nav-link d-flex align-items-center justify-content-center gap-2" do %>
                   <i class="fas fa-sign-in-alt"></i>
                   <%= t('navbar.sign_in') %>
                 <% end %>