Added attribute integrity to head.xsd for linkTypes

As documented here: https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity

Author: erfanimani

lib/internal/Magento/Framework/View/Layout/etc/head.xsd

@@ -20,6 +20,7 @@
         <xs:attribute name="type" type="xs:string"/>
         <xs:attribute name="order" type="xs:integer"/>
         <xs:attribute name="src_type" type="xs:string"/>
+        <xs:attribute name="integrity" type="xs:string"/>
         <xs:attribute name="crossorigin">
             <xs:simpleType>
                 <xs:restriction base="xs:string">