composer.json: fixed minimum requirements

Session use `Nette\Utils\Callback::invokeSafe` which is available in nette/utils since 2.2.2. How did I figure it out?

~~~sh
composer update --prefer-lowest && ./vendor/bin/tester -c ./tests/php-win.ini ./tests/
~~~

The question is – should we check this [automatically](https://github.com/symfony/symfony/commit/ef83a6cd6dae10e7af24329e547c1e3f117ede22)?