Update tubalmartin/cssmin - fixes #8552

Author: sambolek

composer.json

@@ -43,7 +43,7 @@
         "monolog/monolog": "^1.17",
         "oyejorge/less.php": "~1.7.0",
         "pelago/emogrifier": "0.1.1",
-        "tubalmartin/cssmin": "2.4.8-p6",
+        "tubalmartin/cssmin": "2.4.8-p8",
         "magento/magento-composer-installer": ">=0.1.11",
         "braintree/braintree_php": "3.7.0",
         "symfony/console": "~2.3, !=2.7.0",