Update to JGit 4.0.0.201505191015-rc1.19-g1773002

Use try-with-resources to handle clean upreaders and walk
instances that now use close() instead of release().

Change-Id: I884d87715bdd920f4e9ef82864d5b962a5b3b065

gitiles-servlet/src/test/java/com/google/gitiles/PaginatorTest.java

diff --git a/gitiles-servlet/src/test/java/com/google/gitiles/PaginatorTest.java b/gitiles-servlet/src/test/java/com/google/gitiles/PaginatorTest.java
index 2491107..e8af92e 100644
--- a/gitiles-servlet/src/test/java/com/google/gitiles/PaginatorTest.java
+++ b/gitiles-servlet/src/test/java/com/google/gitiles/PaginatorTest.java
@@ -50,7 +50,7 @@
 
   @After
   public void tearDown() throws Exception {
-    walk.release();
+    walk.close();
   }
 
   @Test