Fix section 15.9 quiz

[yaxollum]

For the last question of the Section 15.9 quiz:

• Fixed grammar

• The correct option should be [], not Validation.

  This is what I tested in GHCi:

  
  λ> pure 3 <* pure 4 :: Maybe Int
  Just 3
  λ> pure 3 <|> pure 4 :: Maybe Int
  Just 3

λ> pure 3 <* pure 4 :: Validation Int Ok 3 λ> pure 3 <|> pure 4 :: Validation Int Ok 3

λ> pure 3 <* pure 4 :: [Int] [3] λ> pure 3 <|> pure 4 :: [Int] [3,4]

For the `[]` Applicative, `pure 3 <* pure 4` produces `[3]`, whereas `pure 3 <|> pure 4` produces `[3,4]`.

[opqdonut]

thanks!