Fix failing unit test.

Summary: On PHP versions earlier than 5.4.0, `\e` is not a valid PHP escape character. Consequently, `PhutilUTF8TestCase::testUTF8ConsoleStrlen` will fail. Replace `\e` by its hexadecimal equivalent.

Test Plan: Ran unit tests.

Reviewers: hach-que, epriestley, #blessed_reviewers

Reviewed By: hach-que, epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9615