fix type error (except an int) in jumpmp_search line 7.

[clobob]

Try to run this on Python 2.7.10.
An error occurs, the error log like this:
Traceback (most recent call last):
File "jump_search.py", line 25, in
index = jump_search(arr, x)
File "jump_search.py", line 7, in jump_search
while arr[min(step, n)-1] < x:
TypeError: list indices must be integers, not float

the fix make the code can be run under python2 & python3.