RefServletTest: Fix usage of deprecated Repository#peel method

Change-Id: Iaaea85e15a49a41be2c399805615c9bccb0b795c

javatests/com/google/gitiles/RefServletTest.java

diff --git a/javatests/com/google/gitiles/RefServletTest.java b/javatests/com/google/gitiles/RefServletTest.java
index 8dff6b3..daaa52e 100644
--- a/javatests/com/google/gitiles/RefServletTest.java
+++ b/javatests/com/google/gitiles/RefServletTest.java
@@ -305,7 +305,10 @@
 
   private String peeled(String refName) throws IOException {
     return ObjectId.toString(
-        repo.getRepository().peel(repo.getRepository().exactRef(refName)).getPeeledObjectId());
+        repo.getRepository()
+            .getRefDatabase()
+            .peel(repo.getRepository().exactRef(refName))
+            .getPeeledObjectId());
   }
 
   private Map<String, String> ref(String url, String name) {