fixed bug in SUT preventing running it on Windows

Author: arcuri82

jdk_11_maven/cs/graphql/timbuctoo/timbuctoo-instancev4/src/main/java/nl/knaw/huygens/timbuctoo/v5/datastorage/implementations/filesystem/FileSystemDataStorage.java

@@ -57,7 +57,8 @@ public Map<String, Set<DataSetMetaData>> loadDataSetMetaData() throws IOExceptio
     File[] directories = new File(dataSetMetadataLocation).listFiles(File::isDirectory);
     for (File directory : directories) {
       String dirName = directory.toString();
-      String currentOwnerId = dirName.substring(dirName.lastIndexOf("/") + 1);
+//      String currentOwnerId = dirName.substring(dirName.lastIndexOf("/") + 1);
+      String currentOwnerId = dirName.substring(dirName.lastIndexOf(File.separatorChar) + 1);
       Set<DataSetMetaData> tempMetaDataSet = new HashSet<>();
       try (Stream<Path> fileStream = Files.walk(directory.toPath())) {
         Set<Path> paths = fileStream.filter(current -> Files.isDirectory(current)).collect(Collectors.toSet());