Switch to monotonic clock (#1100)

src/common/common.cc

@@ -71,6 +71,6 @@ char *ObjectID_to_string(ObjectID obj_id, char *id_string, int id_length) {
 int64_t current_time_ms() {
   std::chrono::milliseconds ms_since_epoch =
       std::chrono::duration_cast<std::chrono::milliseconds>(
-          std::chrono::system_clock::now().time_since_epoch());
+          std::chrono::steady_clock::now().time_since_epoch());
   return ms_since_epoch.count();
 }