Sort HEAD ref at the top of the list, not the bottom

Change-Id: I37231767c19f72fbc681cd41367e0d832fd54252

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

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/RefServlet.java b/gitiles-servlet/src/main/java/com/google/gitiles/RefServlet.java
index 6113c13..959a449 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/RefServlet.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/RefServlet.java
@@ -88,7 +88,7 @@
       public int compare(@Nullable Ref left, @Nullable Ref right) {
         int l = isHead(left) ? 1 : 0;
         int r = isHead(right) ? 1 : 0;
-        return l - r;
+        return r - l;
       }
 
       private final boolean isHead(Ref ref) {