Fix the script that saves lint for a repo into the database and updates diffusion.

Summary:
It appears a change to the way the configuration was loaded into ArcanistRepositoryAPI in rARCa2285b2b broke the save_lint script.
This updates the DiffusionLintSaveRunner to use the configuration correctly, allowing the linter to run

Test Plan: cd /your/project; ../../../path/to/phabricator/scripts/repository/save_lint.php

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: aran, epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D8487