add more folders to .gitattributes

[dmaicher]

Fixes https://github.com/elastic/elasticsearch-php/issues/1349

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[cla-checker-service[bot]]

💚 CLA has been signed

[ezimuel]

Thanks @dmaicher and sorry for the late reply.

[ezimuel]

Unfortunately, I needed to remove the docs folder in .gitattributes since it is breaking our internal docs build. I'll investigate more and hopefully revert the change asap.