Build fix

Scope AlphabeticIndex.ImmutableIndex

Bug:
Change-Id: I141e5d6631613fe6460603f1c9d0eb0b32997967
diff --git a/luni/src/test/java/libcore/icu/AlphabeticIndexTest.java b/luni/src/test/java/libcore/icu/AlphabeticIndexTest.java
index 05f24d2..8298460 100644
--- a/luni/src/test/java/libcore/icu/AlphabeticIndexTest.java
+++ b/luni/src/test/java/libcore/icu/AlphabeticIndexTest.java
@@ -191,7 +191,7 @@
       .addLabels(new Locale("ru"));
     assertEquals(MAX_LABEL_COUNT, ai.getMaxLabelCount());
     assertEquals(208, ai.getBucketCount());
-    ImmutableIndex ii = ai.getImmutableIndex();
+    AlphabeticIndex.ImmutableIndex ii = ai.getImmutableIndex();
     assertEquals(ai.getBucketCount(), ii.getBucketCount());
   }