This appears in javadoc

Commit 7efb9090 seems to have done
without paying attention to what javadoc refers to.

core/src/main/java/hudson/model/TaskListener.java

@@ -33,6 +33,7 @@ import java.io.IOException;
 import java.io.PrintStream;
 import java.io.PrintWriter;
 import java.io.Serializable;
+import java.util.Formatter;
 
 /**
  * Receives events that happen during some lengthy operation