Create the function ```consecutive(arr)``` that takes an array of integers and return the minimum number of integers needed to make the contents of ```arr``` consecutive from the lowest number to the highest number.
For example:  If ```arr``` contains [4, 8, 6] then the output should be 2 because two numbers need to be added to the array (5 and 7) to make it a consecutive array of numbers from 4 to 8. Numbers in ```arr``` will be unique.
def consecutive(arr):
    if len(arr) <= 1:
        return 0
    return (max(arr) - min(arr) + 1) - len(arr)
def consecutive(arr):
    if len(arr) <= 1:
        return 0
    return (max(arr) - min(arr) + 1) - len(arr)