[Documentation] Fix warning about version of Sylius in Plus installation guide
[Documentation] Fix warning about version of Sylius in Plus installation guide

loic425/Sylius,antonioperic/Sylius,pamil/Sylius,Arminek/Sylius,Zales0123/Sylius,loic425/Sylius,SyliusBot/Sylius,SyliusBot/Sylius,101medialab/Sylius,Zales0123/Sylius,lchrusciel/Sylius,Sylius/Sylius,diimpp/Sylius,antonioperic/Sylius,Zales0123/Sylius,diimpp/Sylius,Sylius/Sylius,101medialab/Sylius,pamil/Sylius,Arminek/Sylius,101medialab/Sylius,lchrusciel/Sylius,lchrusciel/Sylius,diimpp/Sylius,Arminek/Sylius,SyliusBot/Sylius,pamil/Sylius,antonioperic/Sylius,Sylius/Sylius,loic425/Sylius