Fix --resolution option in `d4tools plot`

[kojix2]

Hi

I have recently tried this tool again since the pull requests were merged. It is very fast to create d4 format files using mosdepth.

I was using the plot subcommand of d4tools and noticed that the --resolution option is ignored.

cargo build
 ./target/debug/d4tools plot --resolution 32x12 d4tools/test/data/input.d4 input.d4.svg --region 1

Actual output

error: Found argument 'input.d4.svg' which wasn't expected, or isn't valid in this context

USAGE:
    plot <input-file> <output-file> --region <chr[:start[-end]]> --resolution

For more information try --help

Expected output

I think the reason for this is that value_name is not specified and the option is set to take no arguments.

Thank you.

[brentp]

thanks! does this fix the issue for you?