HADOOP-13997. Typo in metrics docs (Contributed by Ana Krasteva via Daniel Templeton)

(cherry picked from commit d4483a2fe47ccc589e71c6fe5501878e6142c26f)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/package-info.java

@@ -327,7 +327,7 @@
         <td><pre>
   myprefix.sink.*.class=org.apache.hadoop.metrics2.sink.FileSink
   myprefix.sink.file0.context=context0
-  myprefix.sink.file0.filename=context1.out
+  myprefix.sink.file0.filename=context0.out
   myprefix.sink.file1.context=context1
   myprefix.sink.file1.filename=context1.out
   ...