Fix to replace _rsync with _fileCopy

[abetomo]

In preparation for a problem, processing that can be switched by environment variable is put in place.
If the next version has been released and there are no major problems, Replace with _fileCopy.

[DeviaVir]

Interesting, would it make sense to only use _fileCopy in the case of Windows, and rsync with other platforms? Is there an optimization to be had there?

[abetomo]

@DeviaVir
According to the result of travis-ci, _ fileCopy seems to be a little bit faster.
(It does not measure strictly)
(It will be displayed as XX ms to the right of the test results when it took a long time to test.)

As the difference in speed is really small, should we use _rsync as usual except in Windows?
(There is also an advantage that the influence range is reduced, so will I fix it?)

[DeviaVir]

@abetomo long as fileCopy does not make it smaller, and indeed makes it faster, I'm fine with switching to that. Will merge this PR.

[abetomo]

@DeviaVir Thank you!