s5cmd ls --recursive ... prints error text to stdout

[eigood]

I am converting a workflow from s3cmd to s5cmd, and didn't notice that s5cmd doesn't support recursive. I had redirected the ls to a file(for later processing with shell tools), and the script was failing(via set -e). I would have expected an error to be printed to stderr, like any other tool, so I was initially confused.

If s5cmd detects an error with cmdline arguments, it should print the help text to stderr, not stdout.