chore: update xmlunit to version 2.6.2
chore: update xmlunit to version 2.6.2

https://github.com/xmlunit/xmlunit/blob/master/RELEASE_NOTES.md#xmlunit-for-java-262---released-2018-08-27

Jasig/uPortal,jonathanmtran/uPortal,groybal/uPortal,bjagg/uPortal,cousquer/uPortal,ChristianMurphy/uPortal,cousquer/uPortal,GIP-RECIA/esco-portail,mgillian/uPortal,cousquer/uPortal,GIP-RECIA/esco-portail,groybal/uPortal,ChristianMurphy/uPortal,bjagg/uPortal,groybal/uPortal,mgillian/uPortal,groybal/uPortal,mgillian/uPortal,jonathanmtran/uPortal,groybal/uPortal,jonathanmtran/uPortal,GIP-RECIA/esco-portail,Jasig/uPortal,bjagg/uPortal,Jasig/uPortal,ChristianMurphy/uPortal