Make sure php-ipv6 is recognized as a platform package as well

src/Composer/Repository/PlatformRepository.php

@@ -23,7 +23,7 @@ use Composer\Util\Silencer;
  */
 class PlatformRepository extends ArrayRepository
 {
-    const PLATFORM_PACKAGE_REGEX = '{^(?:php(?:-64bit)?|hhvm|(?:ext|lib)-[^/]+)$}i';
+    const PLATFORM_PACKAGE_REGEX = '{^(?:php(?:-64bit|-ipv6)?|hhvm|(?:ext|lib)-[^/]+)$}i';
 
     /**
      * Defines overrides so that the platform can be mocked