Fix method name typo in new modular transaction text/html mail methods

See PHI1039. See D20057.

src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php

@@ -5000,7 +5000,7 @@ abstract class PhabricatorApplicationTransactionEditor
     return $xaction->getTitleForTextMail();
   }
 
-  private function getBodyForHTMLMail(
+  private function getTitleForHTMLMail(
     PhabricatorApplicationTransaction $xaction) {
     $type = $xaction->getTransactionType();