the `nvm.sh` file assigns and exports an `NVM_CD_FLAGS` variable if it
was sourced from a zsh shell. the fact that it's exported means that
it'll be assigned in all child processes, including the `nvm-exec`
script, which uses bash as the interpreter.
Bash's `cd` command doesn't have a `-q` flag, so if the `NVM_CD_FLAGS`
is assigned `-q`, the script will error out and incorrectly claim that
the node version isn't installed.
this also manifests itself in the `nvm exec` command.
Example:
```console
$ nvm exec 16.14.0 npm --version
Running node v16.14.0 (npm v8.3.1)
/Users/<ME>/.nvm/nvm.sh: line 28: cd: -q: invalid option
cd: usage: cd [-L|[-P [-e]] [-@]] [dir]
both the tree and the node path are required
N/A: version "v16.14.0 -> N/A" is not yet installed.
You need to run "nvm install v16.14.0" to install it before using it.
```
To address this, we unset the `NVM_CD_FLAGS` at the start of the
`nvm-exec` script, before loading `nvm.sh`.
Spike Grobstein
Jordan Harband
Peter Dave Hello
Qiangjun Ran
Thomas Levine
Keiichiro Ui
Koen Punt