fixed namespace + path to conform to psr-0 in case-sensitive filesystem

The service definition ...
``` xml
<service id="theme_modern" class="Ladybug\Theme\Modern\ModernTheme">
    <tag name="ladybug.theme" />
</service>
```
... did not match the path and namespace defined for `lib/Ladybug/Theme/modern/ModernTheme.php` (`modern` vs `Modern`) on case-sensitive os. This caused the following exception:
```
PHP Fatal error:  Uncaught exception 'ReflectionException' with message 'Class Ladybug\Theme\Modern\ModernTheme does not exist' in /home/develop/vendor/symfony/dependency-injection/Symfony/Component/DependencyInjection/ContainerBuilder.php:961
Stack trace:
#0 /home/develop/vendor/symfony/dependency-injection/Symfony/Component/DependencyInjection/ContainerBuilder.php(961): ReflectionClass->__construct('Ladybug\Theme\M...')
#1 /home/develop/vendor/symfony/dependency-injection/Symfony/Component/DependencyInjection/ContainerBuilder.php(495): Symfony\Component\DependencyInjection\ContainerBuilder->createService(Object(Symfony\Component\DependencyInjection\Definition), 'theme_modern')
#2 /home/develop/vendor/symfony/dependency-injection/Symfony/Component/DependencyInjection/ContainerBuilder.php(1009): Symfony\Component\DependencyInjection\ContainerBuilder->get('theme_modern', 1)
#3 /home/develop/vendor/symfony/dependency-injection/Symfony/Component/DependencyInjection/ContainerBuilder.php(1006): Symfony in /home/develop/vendor/symfony/dependency-injection/Symfony/Component/DependencyInjection/ContainerBuilder.php on line 961
```