remove duplication of struct defaults

lib/koans/10_structs.ex

@@ -43,12 +43,12 @@ defmodule Structs do
   end
 
   koan "Use the put_in macro to replace a nested value" do
-    airline = %Airline{plane: %Plane{maker: :boeing}}
+    airline = %Airline{}
     assert put_in(airline.plane.maker, :airbus) == ___
   end
 
   koan "Use the update_in macro to modify a nested value" do
-    airline = %Airline{plane: %Plane{maker: :boeing, passengers: 200}}
+    airline = %Airline{plane: %Plane{passengers: 200}}
     assert update_in(airline.plane.passengers, fn x -> x + 2 end) == ___
   end