Specify the config property of lint-test files as a map

Summary: Self-explanatory. This is implied anyway as we iterate over it with a foreach loop.

Test Plan: arc unit

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11174