S3 upload no longer works without CLI path prefix

[dominickp]

For some windows users, CLI commands (like "aws") can be called within scripter directly without needing to specify the path. By including the CLI Command property and appending it to the prefix with a trailing slash, when the cli path prefix is not included, it results in executing "/aws" when it should execute "aws". Additionally, the slash used here should use the internal function provided by Switch to generate the correct slash for the OS ("/" and "").

https://github.com/open-automation/switch-aws/blob/master/Unpacked/S3%20Upload/S3%20Upload.js#L87