hhvm: fix include_path

The include_path PHP setting was incorrectly set under the 'hhvm.'
hierarchy which does not work:

    $ grep include_path /etc/hhvm/php.ini
    hhvm.include_path = .:/usr/share/php

    $ hhvm -a
    hphpd> print ini_get('include_path');
    print ini_get('include_path');
    "."

It needs to be `include_path` and the value enclosed in double quotes
and then:

    $ grep include_path /etc/hhvm/php.ini
    include_path = ".:/usr/share/php"

    $ hhvm -a
    hphpd> print ini_get('include_path');
    print ini_get('include_path');
    ".:/usr/share/php"

That fix the PHPUnit tests for TimedMediaHandler MediaWiki extension
which uses include('PEAR.php').

Bug: T78556
Change-Id: I6084f49e97c855286b86dbbd6ce8e80e94069492