fix: delete extraneous files from destination directory on Windows

[lynxtaa]

Support custom swapScript. Delete extraneous files from dest dirs.

Unlike linux swap script, windows script doesn't delete files which were deleted from the target. It may cause problems. For example,

Old version: ./server.js

New version: ./server.js ./server/index.js

After autoupdate in Windows: ./server.js ./server/index.js

In this scenario require('./server') will use server.js file from the older version.

Using robocopy /mir instead of xcopy will resolve this problem.

[lynxtaa]

@dsheiko , can you please publish updated version to npm?

[dsheiko]

done