Minor language tweak

[zackkitzmiller]

Not sure if this is preferred, but I think that offline is slightly better than off-line.

By submitting this pull request, I confirm the following:
please fill any appropriate checkboxes, e.g: [X]

• I have read and understood the contributors guide, as well as this entire template.
• I have made only one major change in my proposed changes.
• I have commented my proposed changes within the code.
• I have tested my proposed changes, and have included unit tests where possible.
• I am willing to help maintain this change if there are issues with it later.
• I give this submission freely and claim no ownership.
• It is compatible with the EUPL 1.2 license
• I have squashed any insignificant commits. (git rebase)

Please make sure you Sign Off all commits. Pi-hole enforces the DCO.

---

What does this PR aim to accomplish?:
A detailed description, screenshots (if necessary), as well as links to any relevant GitHub issues

How does this PR accomplish the above?:
A detailed description (such as a changelog) and screenshots (if necessary) of the implemented fix

What documentation changes (if any) are needed to support this PR?:
A detailed list of any necessary changes

---

• You must follow the template instructions. Failure to do so will result in your pull request being closed.
• Please respect that Pi-hole is developed by volunteers, who can only reply in their spare time.