fixed bug in metadata show page; added workaround for blacklight bug

fixes #97 
This turned out to be a bug in blacklight 4.6: projectblacklight/blacklight@8b8b7d06e21dbb606feb4e1efb7136c59d8507ca
However, upgrading blacklight to 4.6 would involve changing the dependencies in sufia, sufia-models and hydra which looked like a huge pain. I added a simple workaround with a comment about it.