Unbreak the build on MacOS

Change-Id: I9144a84842baf1921b8d5808983d8d4e7cde747a

internal/ceres/accelerate_sparse.cc

diff --git a/internal/ceres/accelerate_sparse.cc b/internal/ceres/accelerate_sparse.cc
index 59d9dca..a0d7e85 100644
--- a/internal/ceres/accelerate_sparse.cc
+++ b/internal/ceres/accelerate_sparse.cc
@@ -190,7 +190,7 @@
 template <typename Scalar>
 CompressedRowSparseMatrix::StorageType
 AppleAccelerateCholesky<Scalar>::StorageType() const {
-  return CompressedRowSparseMatrix::LOWER_TRIANGULAR;
+  return CompressedRowSparseMatrix::StorageType::LOWER_TRIANGULAR;
 }
 
 template <typename Scalar>