Add additional information on the PHP engine versions to PHP plugin

It would be nice to use the `<<<<` style string definition method here to make things a little bit more readable. [This](https://github.com/opscode/ohai/blob/495cd710e2f5d0a7131cb415e4a861248bb331ca/spec/unit/loader_spec.rb#L47-L51) is an example of what I'm thinking.