Mistake in first equation below Section 5.2.2 in Chapter 5

[Jarell-Cheong]

The first (left) display equation after Section 5.2.2 is:

$m(X_i,X_i^2)=\beta_0+\beta_1 X_i\beta_2 X_i^2$.

This should be replaced with:

$m(X_i,X_i^2)=\beta_0+\beta_1 X_i+\beta_2 X_i^2$.

(added a missing plus sign)

[mattblackwell]

Fixed in 13f0ca4