Update dependency versions in composer.json

Update the versions of composer dependencies to more contemporary values

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This reflects the newer versions available in each of these packages.

vfsStream has a 1.4.0 stable, so 1.* picks the newest stable version.

phpUnit and phpMD have newer versions that are still compatible with all of our current tests.
Similar with codesniffer.

In my review these newer versions are compatible with all our current tests, and keep us open to upward compatibility.