Use nested namespace

It's a mechanical change to modernize the code base

unit_tests/server/parameters_io.hpp

@@ -7,9 +7,7 @@
 
 #include <ostream>
 
-namespace osrm
-{
-namespace engine
+namespace osrm::engine
 {
 namespace api
 {
@@ -60,7 +58,6 @@ inline std::ostream &operator<<(std::ostream &out, Approach approach)
     out << static_cast<int>(approach);
     return out;
 }
-} // namespace engine
 } // namespace osrm
 
 #endif

unit_tests/server/url_parser.cpp

@@ -3,11 +3,7 @@
 #include <fstream>
 
 // needed for BOOST_CHECK_EQUAL
-namespace osrm
-{
-namespace server
-{
-namespace api
+namespace osrm::server::api
 {
 std::ostream &operator<<(std::ostream &out, const osrm::server::api::ParsedURL &url)
 {
@@ -15,8 +11,6 @@ std::ostream &operator<<(std::ostream &out, const osrm::server::api::ParsedURL &
 
     return out;
 }
-} // namespace api
-} // namespace server
 } // namespace osrm
 
 #include <boost/test/test_tools.hpp>