try to suit ubunto

tools/quantification/convert.cpp

@@ -4,7 +4,7 @@
 #include "src/var_desc.h"
 #include "src/program_desc.h"
 #include <cstdlib>
-#include <string>
+#include <string.h>
 #include <cmath>
 #include <iostream>
 #include <utility>
@@ -13,6 +13,7 @@
 #include "src/protobuf-c.h"
 #include <fstream>
 #include <iostream>
+#include <limits>
 
 
 const size_t kSize64 = sizeof(uint64_t);