Fix for Python3 - ‘/’ -> '//'

[MoienBowen]

Only replaced in file ecpy/utils/root.py.
With $grep -nr ' / ' ./, there are lot of '/', to be check if works under Python 3.

[elliptic-shiho]

What is differences of #9 between #8?

I think we doesn't need to fix / to // because ecpy's field / ring classes having floordiv and truediv. ecpy's code has assumed to using that.

Moreover, even if we didn't fix that, ecpy has passed all test at Python 3 enviroment.

[MoienBowen]

What is differences of #9 between #8?

I think we doesn't need to fix / to // because ecpy's field / ring classes having floordiv and truediv. ecpy's code has assumed to using that.

Moreover, even if we didn't fix that, ecpy has passed all test at Python 3 enviroment.

No different, you can delete the request #8.
In my case, there is a warning for the result which may not be a int. So '//' just force the result into an int.

[elliptic-shiho]

@n00d1e5 In current configuration, Travis CI checks test using Python 3.5.x. so error occurred by try import syntax.
Moreover, I (still) use ecpy at Python 2.x sometimes and I wanna use common codes. so I can't merge this breaking change (but I'll fix testing environment version).