add an int() to make the i/4 be a interger rather than a float

[lkcp]

In python3, a integer divide another interger will generate a float , in "aes.py" , line 58, line 83, if we don not add an int to it ,there will be a TypeError: list indices must be integers or slices, not float

[L3odr0id]

In my pull-request, I already proposed a solution to the same problem. But this repository seems to be dead

[Morris-Wei]

Another more elegant way is
matrix[i // 4].append(byte)

[L3odr0id]

Another more elegant way is matrix[i // 4].append(byte)

Yeah, I did exactly the same thing in #8