Auto merge of #3149 - cardoe:fix-pkgid-cmd, r=alexcrichton

pkgid cmd: fix help msg with multiple packages

When there are multiple versions of a package that match a given spec
the command tells you to re-run it with the `-p` argument which does not
exist. The command appears to work without it properly.

Signed-off-by: Doug Goldstein <cardoe@cardoe.com>