Use Parser.problem instead of Debug.todo (#676)

exercises/concept/paolas-prestigious-pizza/src/PaolasPrestigiousPizza.elm

@@ -22,34 +22,34 @@ type alias Pizza =
 
 priceParser : Parser Int
 priceParser =
-    Debug.todo "Please implement this parser"
+    Parser.problem "Please implement this parser"
 
 
 vegetarianParser : Parser Bool
 vegetarianParser =
-    Debug.todo "Please implement this parser"
+    Parser.problem "Please implement this parser"
 
 
 wordParser : Parser String
 wordParser =
-    Debug.todo "Please implement this parser"
+    Parser.problem "Please implement this parser"
 
 
 ingredientsParser : Parser (List String)
 ingredientsParser =
-    Debug.todo "Please implement this parser"
+    Parser.problem "Please implement this parser"
 
 
 pizzaParser : Parser Pizza
 pizzaParser =
-    Debug.todo "Please implement this parser"
+    Parser.problem "Please implement this parser"
 
 
 menuParser : Parser (List Pizza)
 menuParser =
-    Debug.todo "Please implement this parser"
+    Parser.problem "Please implement this parser"
 
 
 oneIngredientParser : Parser String
 oneIngredientParser =
-    Debug.todo "Please implement this parser"
+    Parser.problem "Please implement this parser"