Add the (2,4,8) template specialization.

Change-Id: I058bcebdd1725031d573404133b184d6f27dc005
diff --git a/internal/ceres/schur_eliminator.cc b/internal/ceres/schur_eliminator.cc
index 2701683..4d9b175 100644
--- a/internal/ceres/schur_eliminator.cc
+++ b/internal/ceres/schur_eliminator.cc
@@ -102,6 +102,11 @@
   }
   if ((options.row_block_size == 2) &&
       (options.e_block_size == 4) &&
+      (options.f_block_size == 8)) {
+    return new SchurEliminator<2, 4, 8>(options);
+  }
+  if ((options.row_block_size == 2) &&
+      (options.e_block_size == 4) &&
       (options.f_block_size == 9)) {
     return new SchurEliminator<2, 4, 9>(options);
   }