Update max length for attribute_code (30 to 255)

According with 'attribute_code' (size 255) see in https://github.com/magento/magento2/blob/develop/app/code/Magento/Eav/Setup/InstallSchema.php#L644 , I update the ATTRIBUTE_CODE_MAX_LENGTH constant value from 30 to 255;

Author: Nolwennig

app/code/Magento/Eav/Model/Entity/Attribute.php

@@ -23,7 +23,7 @@ class Attribute extends \Magento\Eav\Model\Entity\Attribute\AbstractAttribute im
     /**
      * Attribute code max length
      */
-    const ATTRIBUTE_CODE_MAX_LENGTH = 30;
+    const ATTRIBUTE_CODE_MAX_LENGTH = 255;
 
     /**
      * Cache tag