Require PHP 7.2, drop <7.2 in Composer & on CI

[Majkl578]

Same reasons as in doctrine/orm#6529, but parameter type widening seems more important here.

[Ocramius]

@Majkl578 continuousphp pipeline requires updating too

[Majkl578]

Yep I noticed, the build uses 7.1.11... They don't support 7.2 yet apparently: https://continuousphp.com/documentation/php/
I'll ping their support and see if there's any ETA.

[Pierozi]

@Majkl578 I've release the container 7.2 few days ago, not yet documented you can select it by interface

[Majkl578]

@Pierozi Thanks for the info, now that's the support I like. 👍
@Ocramius Can you try changing it here? I don't have permissions for that (can't change anything), thanks.

[Ocramius]

Updated, thanks a lot @Pierozi!

[Ocramius]

🚢