rustfmt binary path in usage string

[tharun208]

rustfmt help command returns usage information in which rustfmt binary path is appended to the usage message. The usage message will be cleaner without the binary's path. I am happy to raise a pr for this if we are okay to remove the path from the usage string.

[calebcartwright]

Thanks for reaching out and your willingness to contribute! I agree it would be nice to clean that up, so feel free to take a pass at a PR.

Note you can add a comment containing the text @rustbot claim to get the issue assigned to you and indicate you'll be working on it

[tharun208]

@rustbot claim