fix: make sure destination uses posix separator instead of win

[ddelgrosso1]

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Fixes #2301 🦕

[danielbankhead]

Perhaps using the OS-specific path.sep would be preferred to prefer POSIX customers' ability to write with \.

Suggested change

	.split(path.win32.sep)
	.split(path.sep)

[danielbankhead]

Maybe the prefix here should be split first to preserve the \ for POSIX (in case customers really want it)

Suggested change

	.join(options.prefix, passThroughOptionsCopy.destination)
	.split(path.win32.sep)
	.join(path.posix.sep);
	.posix.join(...options.prefix.split(path.sep), passThroughOptionsCopy.destination);