Added a Dockerfile to help with using snyk-to-html in pipelines

[garethr]

Packaging snyk-to-html as a Docker image makes using the tool in places
where installing a full Node toolchain is problematic or annoying. The
image also aims to make usage easier by outputting the html on stdout,
rather than writing a file to disk.

Using the -o and -i options the image can be used to read and/or write from
files on disk as well.

[gitphill]

Looks good, could add to README something like:

Using Docker

docker build -t snyk-to-html .
snyk test --json | docker run --rm -i snyk-to-html

[garethr]

If this works for you I'd like to get this set up to build and push to the snyk namespace on Docker Hub. so snyk/snyk-to-html presumably. This would require someone with access to create a token from Docker Hub and then encrypt it in the Travis config. I can add an update to the Travis config which will build and push the image as time permits. Alternatively, we could move this to https://github.com/snyk/snyk-images which is building the new image set.

Happy to update the docs when we settle on the best approach. I'd prefer not to just leave users to build the image and for us to build once.

[snyksec]

🎉 This PR is included in version 1.7.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀