Update platform requirments for PHP 7.1 & PHP 7.2

[nedt]

composer.json lists ~7.0.11 as requirement. Is this on purpose? We've installed on PHP 7.1 with --ignore-platform-reqs and no problems so far. As active development on PHP 7.0 stopped I guess ~5.6.0|>=7.0.11 or ~5.6.0|~7.0.11|~7.1 would be better.

[Cyrill Schumacher]

If you can send me a Pull Request with the change, I'm happy to merge it!

[Wouter van der Loop | Toppy]

#11

[Cyrill Schumacher]

Fixed with PR #11