Add a new translation with Symfony4

[victor-paumier]

Hi !
I am using the bundle with Symfony4 and my translations folder is at the root folder of my project, default location of the version 4.

Thanks to the PR (#331), I am able to import and export translations correctly.
The path store in the lexik_translation_file table is ../translations, well no problem.
But everytime I add a new translation, a new line is added to the lexik_translation_file table with the path value equals to /Resources/translations instead of adding it to the existing lexik_translation_file line matching with same domain and locale. And so my new translation line is never export to the right file.

I am not completely sure that is the best solution, but replacing this line by
(Kernel::MAJOR_VERSION >= 4)?$this->rootDir.'/../translations':$this->rootDir.'/Resources/translations' do the trick.