Require PHP >= 5.6 in composer.json

[ayeshrajans]

Now that we are requiring PHP 5.6, perhaps we can indicate this in the composer.json file bundled?

Attached patch updates the composer.json file and also includes the lock file update with composer update --lock.

Thank you.

[jrf]

LGTM 👍🏻

[desrosj]

In 46200:

Build/Test Tools: Specify PHP 5.6 as the required version of PHP in Composer.

Props ayeshrajans, jrf, netweb.
Fixes #48081.