Add di.xml to fix the notice in the admin

[mikesteeghs]

When using your module, the admin throws the following notice when saving a CMS page or block:

This can be fixed by adding the file etc/di.xml in the module and add the following content:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <virtualType name="DefaultWYSIWYGValidator">
        <arguments>
            <argument name="allowedAttributes" xsi:type="array">
                <item name="loading" xsi:type="string">loading</item>
            </argument>
        </arguments>
    </virtualType>
</config>

[collymore]

Thanks for the feedback @mikesteeghs I did see this message on the test site but thought it was already there in Magento!
I'll update the repo now