Compatibility with newer versions of Symfony (#202)

Newer versions of Symfony Process requires an array as an constructor argument. 
Array was supported already in previous versions (since ~v4).

Author: tmotyl

src/MagentoHackathon/Composer/Magento/Plugin.php

@@ -369,7 +369,7 @@ protected function deployLibraries()
 
             $params = $this->getTheseerAutoloadParams($libraryPath, $autoloadDirectories);
 
-            $process = new Process($executable . $params);
+            $process = new Process([$executable, $params]);
             $process->run();
         }
     }