expected message in ValidatingArrayLoaderTest should also contain psr-4 as allowed key.

tests/Composer/Test/Package/Loader/ValidatingArrayLoaderTest.php

@@ -253,7 +253,7 @@ class ValidatingArrayLoaderTest extends \PHPUnit_Framework_TestCase
                     ),
                 ),
                 array(
-                    'autoload : invalid value (psr0), must be one of psr-0, classmap, files'
+                    'autoload : invalid value (psr0), must be one of psr-0, psr-4, classmap, files'
                 )
             ),
         );