Add a missing override

Change-Id: I6f610d187551fb3dca57912681e0e37eea26723f

internal/ceres/conjugate_gradients_solver.h

diff --git a/internal/ceres/conjugate_gradients_solver.h b/internal/ceres/conjugate_gradients_solver.h
index 79fca51..dc948d2 100644
--- a/internal/ceres/conjugate_gradients_solver.h
+++ b/internal/ceres/conjugate_gradients_solver.h
@@ -64,7 +64,7 @@
  public:
   LinearOperatorAdapter(LinearOperator& linear_operator)
       : linear_operator_(linear_operator) {}
-  ~LinearOperatorAdapter = default;
+  ~LinearOperatorAdapter() override = default;
   void RightMultiplyAndAccumulate(const Vector& x, Vector& y) final {
     linear_operator_.RightMultiplyAndAccumulate(x, y);
   }