If you have tag and content in a single line it produces no padding. Make sure you anchor looks something like:
<li>
<a href="#" class="glyphicon glyphicon-wrench">
Maintenance
</a>
</li>
Or using link_to
<li>
<%= link_to dashboards_path, class: 'glyphicon glyphicon-wrench' do %>
<span>Maintenance</span>
<% end %>
</li>
Though it seems strange but
<a href="#" class="glyphicon glyphicon-wrench">Maintenance</a>
produces no spaces between icon and text