Add serialVersionUID to satisfy SpotBugs

Author: jglick

src/main/java/org/jenkinsci/plugins/workflow/log/BufferedBuildListener.java

@@ -47,6 +47,8 @@
  */
 final class BufferedBuildListener extends OutputStreamTaskListener.Default implements BuildListener, Closeable, SerializableOnlyOverRemoting {
 
+    private static final long serialVersionUID = 1;
+
     private static final Logger LOGGER = Logger.getLogger(BufferedBuildListener.class.getName());
 
     private static final Cleaner cleaner = Cleaner.create(new NamingThreadFactory(new DaemonThreadFactory(), BufferedBuildListener.class.getName() + ".cleaner"));