Fixing depreceated return of methods LoadAnnotationService::process and NzoUrIEncryptorBundle::build

[lucasfoussier]

With the latest Symfony versions, we have some depreceated reported in logs :

deprecation	Method "Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface::process()" might add "void" as a native return type declaration in the future. Do the same in implementation "Nzo\UrlEncryptorBundle\DependencyInjection\Compiler\LoadAnnotationService" now to avoid errors or add an explicit @return annotation to suppress this message.
deprecation	User Deprecated: Method "Symfony\Component\HttpKernel\Bundle\Bundle::build()" might add "void" as a native return type declaration in the future. Do the same in child class "Nzo\UrlEncryptorBundle\NzoUrlEncryptorBundle" now to avoid errors or add an explicit @return annotation to suppress this message.

To fix this, adding the return type void to the following methods fix the issues :

• Nzo\UrlEncryptorBundle\DependencyInjection\Compiler\LoadAnnotationService::process
• Nzo\UrlEncryptorBundle\NzoUrlEncryptorBundle::build

Because of the required php version ^7.1.3 of the bundle and this PR similiraty with #67 it shoud be harmless for all the users of the bundle.

[nayzo]

@lucasfoussier Thanks !