app/views/shared/header/_user_info.html.erb
<a href="<%= user_path(current_user) %>">
<% if current_user.avatar? %>
<%= image_tag current_user.avatar.thumb , class: "avatar", title: current_user.name %>
<% else %>
<div class="avatar placeholder" title="<%= current_user.name %>">
<%= icon 'user'%>
</div>
<% end %>
</a>