Include forgotten header

Include the stdint.h for uint64_t. It compiled on most systems, but
failed on some before.

src/lib/datasrc/memory/segment_object_holder.cc

@@ -17,6 +17,7 @@
 #include <boost/lexical_cast.hpp>
 
 #include <cassert>
+#include <stdint.h>
 
 namespace isc {
 namespace datasrc {