Fixed missing headers in manifold.h

https://github.com/ceres-solver/ceres-solver/issues/739

Change-Id: Ia4079b025c53f75abb7145a4b8f5eacaddf8fc67

include/ceres/manifold.h

diff --git a/include/ceres/manifold.h b/include/ceres/manifold.h
index 5525069..30ecae7 100644
--- a/include/ceres/manifold.h
+++ b/include/ceres/manifold.h
@@ -31,6 +31,8 @@
 #ifndef CERES_PUBLIC_MANIFOLD_H_
 #define CERES_PUBLIC_MANIFOLD_H_
 
+#include <array>
+#include <memory>
 #include <vector>
 
 #include "ceres/internal/disable_warnings.h"