Trivial update to virtualbox.md - 'shutdown' is not the verb, barely the noun.

What does this MR do?

Fixes a few typos

Why was this MR needed?

the English was wrong in one spot, just bad in another

Are there points in the code the reviewer needs to double check?

Nah. Documentation only.

Does this MR meet the acceptance criteria?

• Documentation created/updated
• [o] Added tests for this feature/bug
• [-] In case of conflicts with master - branch was rebased

What are the relevant issue numbers?

none.