cp -r doesn't match linux when destination doesn't exist

[gdw2]

In linux, new_dir and existing_dir are now copies (new_dir didn't exist before):

$ mkdir existing_dir
$ touch existing_dir/foo
$ cp -rf existing_dir new_dir

With shelljs, new_dir/existing_dir and existing_dir are copies. I would expect the linux behavior.

cp('-rf', 'existing_dir', 'new_dir')

[gdw2]

This provides the behavior I expect above (added the trailing slash), but I still think the above scenario represents a valid bug.

cp('-rf', 'existing_dir/', 'new_dir')

[Schoonology]

Agreed and confirmed.

[nfischer]

This should be fixed by #271. Would anyone here be able to confirm that this PR fixes it? As far as I can tell, it seems to be good.