Write a Haskell function named doubleFunc which takes as its
parameter a function f from integers to integers and returns a
function from integers to integers which is always twice f.
For example, using this function I should be able to do the following.
With these definitions, fd 3 should return
2 f(3) = 2 (3 + 5) = 16$ and gd 10
should return 2 (3 * 10) = 60.
f x = x + 5
g x = 3 * x
fd = doubleFunc f
gd = doubleFunc