Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

1.7.3

What operating system and processor architecture are you using (go env)?

N/A

What is your suggestion?

add vendor subcommand for example to mange dependencies inside vendor directory

What did you expect to see?

go vendor golang.org/x/sys download golang.org/x/sys pkg inside vendor directory
go vendor -u golang.org/x/sys update golang.org/x/sys pkg
go vendor -u update all packages
go vendor -l list all packages inside vendor directory
go vendor -d golang.org/x/sys delete golang.org/x/sys pkg