Minor performance tweak in Doclava#makePackageHDF()

Change-Id: I0f9f4eada3f3b640e490d8f0221cbe7af148b06c
diff --git a/src/com/google/doclava/Doclava.java b/src/com/google/doclava/Doclava.java
index 94331ee..e2f7d88 100644
--- a/src/com/google/doclava/Doclava.java
+++ b/src/com/google/doclava/Doclava.java
@@ -718,8 +718,9 @@
     }
 
     int i = 0;
-    for (String s : sorted.keySet()) {
-      PackageInfo pkg = sorted.get(s);
+    for (Map.Entry<String, PackageInfo> entry : sorted.entrySet()) {
+      String s = entry.getKey();
+      PackageInfo pkg = entry.getValue();
 
       if (pkg.isHiddenOrRemoved()) {
         continue;