also persist the schemes property

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | https://github.com/symfony-cmf/RoutingBundle/issues/267
| License       | MIT
| Doc PR        | n/a
i think each single scheme is of type string, thus this should be type="string", no?