Replace deprecated ConcurrentHashSet with recommended Java8

ConcurrentHashMap.newKeySet() in postprocessDocuments()

source/net/yacy/search/schema/CollectionConfiguration.java

@@ -54,7 +54,6 @@ import org.apache.solr.common.SolrDocumentList;
 import org.apache.solr.common.SolrException;
 import org.apache.solr.common.SolrInputDocument;
 import org.apache.solr.common.SolrInputField;
-import org.eclipse.jetty.util.ConcurrentHashSet;
 
 import net.yacy.cora.document.analysis.Classification;
 import net.yacy.cora.document.analysis.Classification.ContentDomain;
@@ -1323,11 +1322,11 @@ public class CollectionConfiguration extends SchemaConfiguration implements Seri
 			final CollectionConfiguration collection, final String collection1query, final Map<String, CRV> rankings,
 			final AtomicInteger allcount) {
 		final Map<String, Long> hostExtentCache = new HashMap<String, Long>(); // a mapping from the host id to the number of documents which contain this host-id
-        final Set<String> uniqueURLs = new ConcurrentHashSet<String>(); // will be used in a concurrent environment
+        final Set<String> uniqueURLs = ConcurrentHashMap.newKeySet(); // will be used in a concurrent environment
         final Set<String> localOmitFields = new HashSet<String>();
         localOmitFields.add(CollectionSchema.process_sxt.getSolrFieldName());
         localOmitFields.add(CollectionSchema.harvestkey_s.getSolrFieldName());
-        final Collection<String> failids = new ConcurrentHashSet<String>();
+        final Collection<String> failids = ConcurrentHashMap.newKeySet();
         final AtomicInteger countcheck = new AtomicInteger(0);
         final AtomicInteger proccount = new AtomicInteger();
         final AtomicInteger proccount_referencechange = new AtomicInteger();