hastads-broadcast-attack.py -> error when exponent is different than 3

[Ewael]

Hey, first of all thank you a lot for this script it works very well.
There is just a little problem when EXPONENT var is different than 3 because at the end the root function is set with 3 directly instead of using EXPONENT var.
That's just a little detail but it could bother some.
Have a nice day.