Fix a pht string
Summary:
This translation string is wrong and causes the following warning when running unit tests:
```
[2015-06-15 16:03:41] ERROR 2: vsprintf(): Too few arguments at [/home/joshua/workspace/github.com/phacility/libphutil/src/internationalization/PhutilTranslator.php:95]
arcanist(head=master, ref.master=956bfa701c36), phabricator(head=master, ref.master=80f11427e576), phutil(head=master, ref.master=3ff84448a916)
#0 vsprintf(string, array) called at [<phutil>/src/internationalization/PhutilTranslator.php:95]
#1 PhutilTranslator::translate(string)
#2 call_user_func_array(array, array) called at [<phutil>/src/internationalization/pht.php:17]
#3 pht(string) called at [<phabricator>/src/applications/auth/controller/PhabricatorAuthStartController.php:75]
#4 PhabricatorAuthStartController::handleRequest(AphrontRequest) called at [<phabricator>/src/aphront/AphrontController.php:69]
#5 AphrontController::delegateToController(PhabricatorAuthStartController) called at [<phabricator>/src/applications/base/controller/PhabricatorController.php:213]
#6 PhabricatorController::willBeginExecution() called at [<phabricator>/src/applications/base/controller/__tests__/PhabricatorAccessControlTestCase.php:270]
#7 PhabricatorAccessControlTestCase::checkAccess(string, PhabricatorTestController, AphrontRequest, array, array) called at [<phabricator>/src/applications/base/controller/__tests__/PhabricatorAccessControlTestCase.php:112]
#8 PhabricatorAccessControlTestCase::testControllerAccessControls()
#9 call_user_func_array(array, array) called at [<arcanist>/src/unit/engine/phutil/PhutilTestCase.php:492]
#10 PhutilTestCase::run() called at [<arcanist>/src/unit/engine/PhutilUnitTestEngine.php:65]
#11 PhutilUnitTestEngine::run() called at [<arcanist>/src/workflow/ArcanistUnitWorkflow.php:186]
#12 ArcanistUnitWorkflow::run() called at [<arcanist>/scripts/arcanist.php:382]
```
Test Plan: `arc lint`
Reviewers: epriestley, #blessed_reviewers, chad
Reviewed By: #blessed_reviewers, chad
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D13292