Fix answer to Chapter 3 - Exercise 4 (c)-(d)

The training RSS is going to be lower for the more flexible model
b/c it better follows points and absorbs deviations due to epsilon.
Look at Figure~2.9 for the traning MSE
Merge pull request #31 from ksamdev/ch3/ex4

Fix answer to Chapter 3 - Exercise 4 (c)-(d)