Minor formatting changes to `ArcanistSpellingDefaultData`.

Summary:
Fixed a few minor nitpicks:

  - Fix indentation.
  - Change double quotes to single quotes.
  - Add trailing commas to arrays.

Test Plan: Meh.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9053