Update vendored dependencies

[stanislav-tkach]

Perhaps I'm missing something, but there is no easy way to update vendored dependencies. cargo update would lead to the "failed to select a version for the requirement..." error, so I'm doing the following:

• remove .cargo/config.toml
• use cargo update
• use cargo vendor again

It would be nice to have a separate command or an additional option for the cargo vendor (or cargo update) command that would allow to update vendored dependencies. Ideally, that new command should support the --package options as cargo update does.