Symfony cache lock strategy

[josuealcalde]

I have added a Lock Strategy using Symfony Cache.

The code is really simple.

The drawback is it needs symfony/cache added as dependency.

I have tested it in my project with symfony 4.4.

[wachterjohannes]

@josuealcalde the code looks great - but the tests fail with composer update --prefer-lowest i think the cache component of symfony does not exists in symfony 2.8 - as we will release this in 2.0 we can do breaking changes and i would say remove this from composer and do ^3.4 for symfony dependencies