Changed to use futimes instead of utimes

[ibobo]

As stated here utimes has 1 second resolution, whereas futimes has 1 microsecond resolution.
Since stat also has a 1 microsecond resolution, this caused conditional builds (with gulp-newer for instance) to always rebuild files on platforms with 1 microsecond timestamps for files (Linux with ext2/3).

[richardlawley]

The idea sounds fine, but the tests fail on Windows. If you can fix it so it works on both, I'll merge it in.

[ibobo]

I fixed the tests on my machine: they were failing because when the first test copied the files their atime was updated also, causing a difference with the reference.
I tried sending some more changes, but I cannot understand what's wrong with appVeyor, sorry. Hope you can take a look.
I tested the branch on Mac and Linux: the test goes fine and the code run correctly; the problems on appVeyor seem related to file permissions.

[richardlawley]

I don't think the problem is related to file permissions, but the tests fail on my Windows machine in the same way that they do on appveyor (I believe appveyor is running on Windows). I've spent a little time this morning trying to fix it on Windows, and I can't get it to work.

[ibobo]

I found the time to make it work on Windows, the file had to be opened for writing (so I used 'a' mode instead of 'r')

[richardlawley]

Thanks, that makes sense! Published to NPM as 1.1.0.