Write a function that accepts base (decimal), height (decimal) and shape ("triangle", "parallelogram") as input and calculates the area of that shape.
area_shape(2, 3, "triangle") ➞ 3
area_shape(8, 6, "parallelogram") ➞ 48
area_shape(2.9, 1.3, "parallelogram") ➞ 3.77
0.5 * b * hb * hshape.