Remove unnecessary method call in events view

Since `User#to_param` already returns `User#username`, we don't need to
pass in the user's username. Changing this also helps us obey LoD.

app/views/events/_event.html.haml

@@ -5,7 +5,7 @@
 
     = cache [event, current_application_settings, "v2.2"] do
       - if event.author
-        = link_to user_path(event.author.username) do
+        = link_to user_path(event.author) do
           = image_tag avatar_icon(event.author_email, 40), class: "avatar s40", alt:''
       - else
         = image_tag avatar_icon(event.author_email, 40), class: "avatar s40", alt:''