Use try-with-resources when iterating ovef fiels

Usage of `Files.walk()` requires a try-with-resources in order to
clearly close the stream when walk if finished or exception occurs.

Change-Id: I6d1c29b51f69488cff1058ab6f15b425fc4a737c

src/main/java/com/googlesource/gerrit/plugins/gitrepometrics/collectors/FSMetricsCollector.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/gitrepometrics/collectors/FSMetricsCollector.java b/src/main/java/com/googlesource/gerrit/plugins/gitrepometrics/collectors/FSMetricsCollector.java
index c5f6dc4..f73de6c 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/gitrepometrics/collectors/FSMetricsCollector.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/gitrepometrics/collectors/FSMetricsCollector.java
@@ -21,10 +21,12 @@
 import java.io.File;
 import java.io.IOException;
 import java.nio.file.Files;
+import java.nio.file.Path;
 import java.util.HashMap;
 import java.util.Objects;
 import java.util.concurrent.ExecutorService;
 import java.util.function.Consumer;
+import java.util.stream.Stream;
 import org.eclipse.jgit.internal.storage.file.FileRepository;
 
 public class FSMetricsCollector implements MetricsCollector {
@@ -105,9 +107,9 @@
   private HashMap<GitRepoMetric, Long> filesAndDirectoriesCount(
       FileRepository repository, String projectName) {
 
-    try {
+    try (Stream<Path> objDir = Files.walk(repository.getObjectsDirectory().toPath())) {
       MetricsRecord metricsRecord =
-          Files.walk(repository.getObjectsDirectory().toPath())
+          objDir
               .map(
                   path -> {
                     File f = path.toFile();