Update exec() to use --update=none instead of deprecated option "-n"

[josefglatz]

exec('cp ' . ($overwrite === false ? '-n ' : '') . $fromPath . ' ' . $toPath); uses a deprecated cp option "-n". This leads to warnings

cp: warning: behavior of -n is non-portable and may change in future; use --update=none instead

used cp version cp (GNU coreutils) 9.4