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/solvers/sparse_convex.h b/frc971/solvers/sparse_convex.h
index 9695431..074f2f3 100644
--- a/frc971/solvers/sparse_convex.h
+++ b/frc971/solvers/sparse_convex.h
@@ -9,8 +9,7 @@
 #include "glog/logging.h"
 #include <Eigen/Sparse>
 
-namespace frc971 {
-namespace solvers {
+namespace frc971::solvers {
 
 // TODO(austin): Steal JET from Ceres to generate the derivatives easily and
 // quickly?
@@ -118,7 +117,6 @@
                         std::string_view prefix, int verbosity);
 };
 
-}  // namespace solvers
-}  // namespace frc971
+}  // namespace frc971::solvers
 
 #endif  // FRC971_SOLVERS_SPARSE_CONVEX_H_