Nest all namespaces

The compiler supports this now.  We can type less going forward.
No functional changes.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I29d6fa4f9aacc0e381f1a7637294db0392466995
diff --git a/y2019/jevois/serial.h b/y2019/jevois/serial.h
index 14e2f98..04114cc 100644
--- a/y2019/jevois/serial.h
+++ b/y2019/jevois/serial.h
@@ -1,12 +1,10 @@
 #ifndef Y2019_JEVOIS_SERIAL_H_
 #define Y2019_JEVOIS_SERIAL_H_
 
-namespace y2019 {
-namespace jevois {
+namespace y2019::jevois {
 
 int open_via_terminos(const char *tty_name);
 
-}  // namespace jevois
-}  // namespace y2019
+}  // namespace y2019::jevois
 
 #endif  // Y2019_JEVOIS_SERIAL_H_