fix: use correct SpringUtils class

Author: Dominick Leppich

module-base/src/main/java/de/intranda/goobi/plugins/PDFExtractionPlugin.java

@@ -48,6 +48,7 @@
 import org.apache.commons.io.FileUtils;
 import org.apache.commons.io.FilenameUtils;
 import org.apache.commons.lang.mutable.MutableInt;
+import org.apache.commons.lang3.StringUtils;
 import org.apache.log4j.Logger;
 import org.goobi.beans.Process;
 import org.goobi.beans.Processproperty;
@@ -78,7 +79,6 @@
 import de.sub.goobi.helper.exceptions.SwapException;
 import de.sub.goobi.persistence.managers.PropertyManager;
 import net.xeoh.plugins.base.annotations.PluginImplementation;
-import spark.utils.StringUtils;
 import ugh.dl.DocStruct;
 import ugh.dl.DocStructType;
 import ugh.dl.FileSet;