remove Serializable

src/main/java/org/codelibs/fess/exec/Crawler.java

@@ -19,7 +19,6 @@ import static org.codelibs.core.stream.StreamUtil.stream;
 
 import java.io.File;
 import java.io.IOException;
-import java.io.Serializable;
 import java.lang.management.ManagementFactory;
 import java.text.SimpleDateFormat;
 import java.util.ArrayList;