Your requirements could not be resolved to an installable set of packages.
Problem 1
- symfony/http-kernel[v4.4.30, ..., 4.4.x-dev] require symfony/event-dispatcher ^4.4 -> found symfony/event-dispatcher[v4.4.0-BETA1, ..., 4.4.x-dev] but these were not loaded, likely because it conflicts with another require.
- symfony/http-kernel[v4.4.0-BETA1, ..., v4.4.29] require symfony/error-handler ^4.4 -> found symfony/error-handler[v4.4.0-BETA1, ..., 4.4.x-dev] but these were not loaded, likely because it conflicts with another require.
- Root composer.json requires symfony/http-kernel ^4.4 -> satisfiable by symfony/http-kernel[v4.4.0-BETA1, ..., 4.4.x-dev].