Change strings offset size from 8 bits to 16 bits

tests/unit/test_assignment_opcode.c

@@ -46,7 +46,7 @@ main( int __unused argc,
   const char *strings[] = { "a",
                             "b" };
   int nums [] = { 2 };
-  uint8_t offset = serializer_dump_strings( strings, 2);
+  uint16_t offset = serializer_dump_strings( strings, 2);
   serializer_dump_nums( nums, 1, offset, 2);
 
   init_int( test_program);