Bump requirements to PHP 7.1

[retlehs]

PHP 5.6 and 7.0 are no longer supported

http://php.net/supported-versions.php

ref https://twitter.com/rootswp/status/1068635955936907265
ref #267

[drzraf]

While I understand the reasoning and votes behind this merge, I think its a bad decision.

Debian, for the first time in its history does not provide a version of PHP supported by upstream. But, by definition, provides (security) support for the software bundled (PHP being one of them).

For that reason, even if upstream dropped support <7.1 I believe distribution must be fairly considered too.
Debian does support PHP 7.0, but none of the above version are available in Debian stable.

Since almost no one run PHP binary outside a Linux distribution I believe the PHP requirement should be set to >= 7.0 until this version get obsoleted (not as in "upstream speech" but as in "people uses and server boxes")

I also think it's bad use of composer require which is not intended for politics about what people install on their servers but rather only which dependencies and versions **this** software needs to run correctly

[swalkinshaw]

@drzraf fair points. However, Bedrock is still a boilerplate basically. It's intended to be customized as you need. It's also not a framework you upgrade in the traditional sense. So for anyone who used an older version of Bedrock as a starting point, this wouldn't affect them.

And if you're starting a new project on an OS which doesn't provide 7.1 (like Debian), you can either use a slightly older version or just manually edit composer.json.

We still believe this is a sensible default to have considering how Bedrock is used.