chore(composer): Update PHPCS minimum version to 2.8.1 after upstream security fix

composer.json

@@ -12,7 +12,7 @@
     "require": {
         "php": ">=5.4.0",
         "ext-mbstring": "*",
-        "squizlabs/php_codesniffer": ">=2.7.0 <3.0",
+        "squizlabs/php_codesniffer": ">=2.8.1 <3.0",
         "symfony/yaml": ">=2.0.0"
     },
     "require-dev": {