Textual error

Hi!

In your Parser Combinators text you have what seems to be a typo:

> To accommodate this pattern, we're going to use our pair combinator to write two other combinators: `left, which discards the result of the first parser and only returns the second`, and its opposite number, right, which is the one we'd have wanted to use in our test above instead of pair - the one that discards that () on the left hand side of the pair and only keeps our String.

`left` actually discards the second result and returns the first, while `right` does what it says.