Apply suggestion from @josevalim

Author: josevalim

lib/plug/conn.ex

@@ -1436,12 +1436,9 @@ defmodule Plug.Conn do
   end
 
   defp adapter_inform(%Conn{adapter: {adapter, payload}}, status, headers) do
-    headers =
-      for {key, value} <- headers do
-        key = to_string(key)
-        validate_header_key_value!(key, value)
-        {key, value}
-      end
+    for {key, value} <- headers do
+      validate_header_key_value!(to_string(key), value)
+    end
 
     adapter.inform(payload, status, headers)
   end