Update Highlight.php

[Surt]

https://github.com/babenkoivan/scout-elasticsearch-driver/issues/152

[iget-esoares]

Hi @Surt,

Could you please describe your changes and reasons?

Also would be greate to have tests for your changes.

[Surt]

Hi @iget-esoares it was just a quick proposal. It adds \ArrayAccess, \Iterator to the Highlight results object. Now it is possible to transverse throught the hightlighted results with a foreach. As well as accesing the results as it was an Array.

I'm not having the necesary time right now. I will try to make an adecuate pull request someday if nobody take it from here.

By the way, looking again i see it could be done easily just setting $highlight property as public ....