Fix doi in solr document

hyrax/app/models/solr_document.rb

@@ -39,7 +39,7 @@ class SolrDocument
   end
 
   def doi
-    self[Solrizer.solr_name('doi', :stored_searchable)]
+    self[Solrizer.solr_name('doi', :symbol)]
   end
 
   def complex_relation