change of Silex namespace in KnpMenu

Updated namespaces for all the Silex folder in KnpMenu

See:
https://github.com/KnpLabs/KnpMenu/commit/47a2233f93831fed2e27f205eb771ca2e40efe95
and
https://github.com/KnpLabs/KnpMenu/commit/c196a37de14e46f89b4fef86c22e1dd44ea1db02