Fix visiblity of LiskDAO::getConfiguration()

Summary: Ref T6822.

Test Plan: `grep`

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: hach-que, Korvin, epriestley

Maniphest Tasks: T6822

Differential Revision: https://secure.phabricator.com/D11370

src/applications/differential/storage/DifferentialTransactionComment.php

@@ -16,7 +16,7 @@ final class DifferentialTransactionComment
     return new DifferentialTransaction();
   }
 
-  public function getConfiguration() {
+  protected function getConfiguration() {
     $config = parent::getConfiguration();
     $config[self::CONFIG_COLUMN_SCHEMA] = array(
       'revisionPHID' => 'phid?',