Replace call to deprecated RevWalk.release() in DescribeCommand

Change-Id: Ie4bfdeb37d345d6ff1525a737f3b7653b2f8e23e
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/api/DescribeCommand.java

@@ -315,7 +315,7 @@ public class DescribeCommand extends GitCommand<String> {
 			throw new JGitInternalException(e.getMessage(), e);
 		} finally {
 			setCallable(false);
-			w.release();
+			w.close();
 		}
 	}
 }