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