add current sign-in date

add current sign-in date to admin section profile view

app/views/admin/users/show.html.haml

@@ -70,6 +70,14 @@
                 %strong.cred
                   No
 
+            %li
+              %span.light Current sign-in at:
+              %strong
+                - if @user.current_sign_in_at
+                  = @user.current_sign_in_at.stamp("Nov 12, 2031")
+                - else
+                  never
+
             %li
               %span.light Last sign-in at:
               %strong