Switch RevWalker from release to close

Gerrit's JGit has been updated to a version without 'release'. Hence,
we update to using 'close' instead.

(After this commit, the code compiles again. Updating to AutoClosable
is done in follow-up commits, after the exception catching got cleaned
up a bit.)

Change-Id: I8910c314f01b09238c960c01af21c61890600674
diff --git a/src/main/java/com/googlesource/gerrit/plugins/reviewersbyblame/ChangeUpdatedListener.java b/src/main/java/com/googlesource/gerrit/plugins/reviewersbyblame/ChangeUpdatedListener.java
index 59bb3b4..d21d5c3 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/reviewersbyblame/ChangeUpdatedListener.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/reviewersbyblame/ChangeUpdatedListener.java
@@ -191,7 +191,7 @@
     } catch (OrmException x) {
       log.error(x.getMessage(), x);
     } finally {
-      rw.release();
+      rw.close();
       git.close();
     }
   }