Use PHP_OS_FAMILY if possible

Author: javiereguiluz

DebugClassLoader.php

@@ -208,7 +208,7 @@ public function __construct(callable $classLoader)
             } elseif (substr($test, -\strlen($file)) === $file) {
                 // filesystem is case insensitive and realpath() normalizes the case of characters
                 self::$caseCheck = 1;
-            } elseif (false !== stripos(\PHP_OS, 'darwin')) {
+            } elseif ('Darwin' === \PHP_OS_FAMILY) {
                 // on MacOSX, HFS+ is case insensitive but realpath() doesn't normalize the case of characters
                 self::$caseCheck = 2;
             } else {