Validate dockerfile

In some point there is a need to validate if a Dockerfile is correctly structured, well there is a package to do that, if Dockerfile files are going to be maintained here.

The following website indicate how to use it https://www.npmjs.com/package/validate-dockerfile

targeting to docklint as the following (using it) https://github.com/Runnable/validate-dockerfile/blob/master/bin/docklint

Let me know your comments