Update add_and_remove_assignee_responder.rb

Let's use only one i.

Author: RichardLitt

app/responders/add_and_remove_assignee_responder.rb

@@ -13,7 +13,7 @@ def process_message(message)
     add_or_remove = @match_data[1].downcase
     user = @match_data[2]
 
-    iif ["add", "assign"].include?(add_or_remove)
+    if ["add", "assign"].include?(add_or_remove)
       add user
     elsif add_or_remove == "remove"
       remove user