Make doMath calculation consistent with earlier examples

[janekdb]

This makes the doMath example consistent with the earlier examples where 1 is added and then the result is multiplied by 2,

val func1 = (a: Int) => a + 1
val func2 = (a: Int) => a * 2
val func3 = (a: Int) => s"${a}!"
val func4 = func1.map(func2).map(func3)