Show invalid unlock token message

Attribute unlock token is not present in the simple_form template,
therefore not being displayed by #error_notification.
This fix explicitily call #full_error on :unlock_token.

lib/generators/templates/simple_form_for/unlocks/new.html.erb

@@ -2,6 +2,7 @@
 
 <%= simple_form_for(resource, :as => resource_name, :url => unlock_path(resource_name), :html => { :method => :post }) do |f| %>
   <%= f.error_notification %>
+  <%= f.full_error :unlock_token %>
 
   <div class="form-inputs">
     <%= f.input :email, :required => true, :autofocus => true %>