Fix typo in exit_status

[aveyrenc]

What does this PR do

Fix a typo in exit_status.

Maybe fixes issue #930

Standards checklist

• The PR title is descriptive.
• I have read CONTRIBUTING.md
• Optional: I have tested the code myself

Output of failing step before patch:

── 21:46:00 - Brew ─────────────────────────────────────────────────────────────
Brew failed: 
   0: Command failed: `brew update`
   1: `brew` failed: %{exit_satus}

Location:
   src/steps/os/unix.rs:335
Retry? (y)es/(N)o/(s)hell/(q)uit

After patch:

── 21:44:47 - Brew ─────────────────────────────────────────────────────────────
Brew failed: 
   0: Command failed: `brew update`
   1: `brew` failed: exit status: 1

Location:
   src/steps/os/unix.rs:335
Retry? (y)es/(N)o/(s)hell/(q)uit

For new steps

• Optional: Topgrade skips this step where needed
• Optional: The --dry-run option works with this step
• Optional: The --yes option works with this step if it is supported by
  the underlying command

If you developed a feature or a bug fix for someone else and you do not have the
means to test it, please tag this person here.

[SteveLauC]

Thanks!

I am working on an i18n checker, but checking arguments has not been implemented yet. 😪