RepositoryIndexServlet: Make renderReadme() static

Change-Id: I7c128be91481ab1c068f5679c86c4fc51e644ea9

gitiles-servlet/src/main/java/com/google/gitiles/RepositoryIndexServlet.java

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/RepositoryIndexServlet.java b/gitiles-servlet/src/main/java/com/google/gitiles/RepositoryIndexServlet.java
index 2965923..32359db 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/RepositoryIndexServlet.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/RepositoryIndexServlet.java
@@ -130,8 +130,8 @@
     return list.size() > REF_LIMIT ? list.subList(0, REF_LIMIT) : list;
   }
 
-  private Map<String, Object> renderReadme(RevWalk walk, GitilesView view,
-      Config cfg, RevObject head) throws IOException {
+  private static Map<String, Object> renderReadme(RevWalk walk,
+      GitilesView view, Config cfg, RevObject head) throws IOException {
     RevTree rootTree;
     try {
       rootTree = walk.parseTree(head);