Use nested namespace

It's a mechanical change to modernize the code base

src/storage/io_config.cpp

@@ -6,9 +6,7 @@
 #include <boost/filesystem/operations.hpp>
 #include <boost/filesystem/path.hpp>
 
-namespace osrm
-{
-namespace storage
+namespace osrm::storage
 {
 
 namespace fs = boost::filesystem;
@@ -40,5 +38,4 @@ std::vector<std::string> IOConfig::GetMissingFiles() const
     }
     return missingFiles;
 }
-} // namespace storage
 } // namespace osrm

src/storage/storage.cpp

@@ -36,9 +36,7 @@
 #include <new>
 #include <string>
 
-namespace osrm
-{
-namespace storage
+namespace osrm::storage
 {
 namespace
 {
@@ -587,5 +585,4 @@ void Storage::PopulateUpdatableData(const SharedDataIndex &index)
         }
     }
 }
-} // namespace storage
 } // namespace osrm