Add a missing header

Change-Id: I26705eb557a8e21b6acc7d18a01471d38a3c1c23

internal/ceres/coordinate_descent_minimizer.h

diff --git a/internal/ceres/coordinate_descent_minimizer.h b/internal/ceres/coordinate_descent_minimizer.h
index 7c27f8c..382885f 100644
--- a/internal/ceres/coordinate_descent_minimizer.h
+++ b/internal/ceres/coordinate_descent_minimizer.h
@@ -31,6 +31,7 @@
 #ifndef CERES_INTERNAL_COORDINATE_DESCENT_MINIMIZER_H_
 #define CERES_INTERNAL_COORDINATE_DESCENT_MINIMIZER_H_
 
+#include <memory>
 #include <string>
 #include <vector>