Remove 0 margin bottom for last paragraph on note text

What does this MR do?

Adds margin back to last paragraph of note text. Introduced here: https://gitlab.com/gitlab-org/gitlab-ce/commit/ab91f76e8b275d0fc1d78b38b95d4b2cd8e73bdb

Screenshots (if relevant)

Before:

After:

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?