fix Zend framework library path

The Zend framework Autoloader is located in ``library/Zend/Loader/``
within the Zend sub-module. Fix the include path in index.php to match
the extra ``library``.

[1] https://github.com/zendframework/zf1/tree/master/library/Zend/Loader
Merge pull request #182 from rjw57/fix-zend-library-path

SPECULATIVE: fix Zend framework library path