Get rid of deprecations

[jmsche]

Q	A
Bug fix?	no
New feature?	no
Tests pass?	yes
Fixed tickets	N/A

Hi, this PR fixes the following deprecations I get:

• Method "Symfony\Component\DependencyInjection\Extension\ExtensionInterface::load()" might add "void" as a native return type declaration in the future. Do the same in implementation "Kocal\BiomeJsBundle\DependencyInjection\BiomeJsExtension" now to avoid errors or add an explicit @return annotation to suppress this message.
• Method "Symfony\Component\Console\Command\Command::initialize()" might add "void" as a native return type declaration in the future. Do the same in child class "Kocal\BiomeJsBundle\Command\BiomeJsCiCommand" now to avoid errors or add an explicit @return annotation to suppress this message.
• Method "Symfony\Component\Console\Command\Command::initialize()" might add "void" as a native return type declaration in the future. Do the same in child class "Kocal\BiomeJsBundle\Command\BiomeJsCheckCommand" now to avoid errors or add an explicit @return annotation to suppress this message.

[Kocal]

Thank you! :)