Fix deprecated on tree builder root

[maximecolin]

Fix the following deprecation :

A tree builder without a root node is deprecated since Symfony 4.2 and will not be supported anymore in 5.0.

The "Symfony\Component\Config\Definition\Builder\TreeBuilder::root()" method called for the "m6_statsd" configuration is deprecated since Symfony 4.3, pass the root name to the constructor instead.

See https://github.com/symfony/symfony/blob/4.4/src/Symfony/Component/Config/Definition/Builder/TreeBuilder.php#L30

[Oliboy50]

Suggested change

	"symfony/property-access": "^3.4 || ^4.0",
	"symfony/property-access": "^4.0",

let's also remove support for symfony 3.4 here, we'll bump a new major release anyway

to make the CI build pass, we will have to tell travis to also stop building using SYMFONY_VERSION: 3.4...
I'd suggest to use SYMFONY_VERSION: 4.4 to be prepared for symfony 5

[Oliboy50]

I've rebased and updated a few things after the merge of #75 which drop support for everything below symfony 4.4

[Oliboy50]

thank you 👌

=> https://packagist.org/packages/m6web/statsd-bundle#v4.0.0