Nest some more namespaces

Did someone previously suggest that all namespace had been
nested?  Silly.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I22278c1caaeba8b47dc46fb2ed3078c20a11e190
diff --git a/frc971/control_loops/runge_kutta.h b/frc971/control_loops/runge_kutta.h
index 7fa3f3e..ed5a359 100644
--- a/frc971/control_loops/runge_kutta.h
+++ b/frc971/control_loops/runge_kutta.h
@@ -3,8 +3,7 @@
 
 #include <Eigen/Dense>
 
-namespace frc971 {
-namespace control_loops {
+namespace frc971::control_loops {
 
 // Implements Runge Kutta integration (4th order).  fn is the function to
 // integrate.  It must take 1 argument of type T.  The integration starts at an
@@ -67,7 +66,6 @@
   return X + dt / 6.0 * (k1 + 2.0 * k2 + 2.0 * k3 + k4);
 }
 
-}  // namespace control_loops
-}  // namespace frc971
+}  // namespace frc971::control_loops
 
 #endif  // FRC971_CONTROL_LOOPS_RUNGE_KUTTA_H_