Users of `zsh` can define hook functions that execute when
the current directory changes. If a user has their `zsh`
configured with a hook function that writes to stdout, the
`asdf` setup script will capture that output in addition to
the output of `pwd`, which causes a misconfiguration of the
`PATH` environment variable.
By redirecting the output, if any, of the `cd` command to
`/dev/null`, this ensures that the path to `bin` in `asdf`
is captured correctly regardless of `zsh` configuration.
Referred a couple other version managers. The advantage is not having to
maintain the scripts for other shells (bash comes by default everywhere
I've seen).
