Adjust the server time format with the client one in ClientGuide

Server and client request/responce time format differs, since
std::chrono::time_point::time_since_epoch() output contains
undeterminated units. Make the explicit conversion to milliseconds,
to align the time format between server and client.

Pick-to: 6.8 6.9
Change-Id: I5914221d3b3b8043721f4d97705ccb54c679be9c
Reviewed-by: Dennis Oberst <dennis.oberst@qt.io>

examples/grpc/clientguide/server/main.cpp

@@ -20,7 +20,9 @@ namespace {
 
 int64_t now()
 {
-    return std::chrono::system_clock::now().time_since_epoch().count();
+    return std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now()
+                                                                     .time_since_epoch())
+        .count();
 }
 
 std::ostream &operator<<(std::ostream &stream, const Request &request)