Use Composer autoloader in the PHAR.

Since the PHAR includes dependencies, we must use Composer's autoloader.
It ensures all dependencies will be loaded correctly and as expected.

phar/stub.php

@@ -34,7 +34,7 @@
  */
 
 Phar::mapPhar("solarium.phar");
-require_once 'phar://solarium.phar/library/Solarium/Autoloader.php';
+require_once 'phar://solarium.phar/vendor/autoload.php';
 Solarium\Autoloader::register();
 
 if ('cli' === php_sapi_name() && basename(__FILE__) === basename($_SERVER['argv'][0]) && isset($_SERVER['argv'][1])) {