Change syntax highlighting for custom phabricator dot configs

Test Plan:
Created new paste with title '.arcconfig' without choosing a language; observed that the paste gets highlighted as JSON.

JSON mode:
{F4901762}

Javascript mode:
{F4901763}

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T11667

Differential Revision: https://secure.phabricator.com/D17682

src/applications/config/option/PhabricatorSyntaxHighlightingConfigOptions.php

@@ -122,9 +122,9 @@ final class PhabricatorSyntaxHighlightingConfigOptions
         'syntax.filemap',
         'wild',
         array(
-          '@\.arcconfig$@' => 'js',
-          '@\.arclint$@' => 'js',
-          '@\.divinerconfig$@' => 'js',
+          '@\.arcconfig$@' => 'json',
+          '@\.arclint$@' => 'json',
+          '@\.divinerconfig$@' => 'json',
         ))
         ->setSummary(
           pht('Override what language files (based on filename) highlight as.'))