Replaced \Symfony\Component\HttpKernel\Log\LoggerInterface with \Psr\Log\LoggerInterface.
Added psr/log to composer.json.

Symfony advises to use \Psr\Log\LoggerInterface instead of the \Symfony\Component\HttpKernel\Log\LoggerInterface. Since the symfony loggerInterface is deprecated and to be removed in 3.0.

since 2.2, to be removed in 3.0. Type-hint .