Load polyfill from application, not from composer'

This way the polyfill won't be executed when
php-parallel-lint is loaded as composer dependency
but in application only.

Author: glensc

Diff for: composer.json

@@ -29,7 +29,6 @@
         "sort-packages": true
     },
     "autoload": {
-        "files": [ "src/polyfill.php" ],
         "classmap": [
             "./"
         ]

Diff for: parallel-lint

@@ -61,5 +61,7 @@ if (!$loaded) {
     exit(254);
 }
 
+require_once __DIR__ . '/src/polyfill.php';
+
 $app = new JakubOnderka\PhpParallelLint\Application();
 exit($app->run());