upgrade flow-website docker image to ruby 2.6, node 12, jre 11
upgrade flow-website docker image to ruby 2.6, node 12, jre 11

Summary:
```
docker build -t flowtype/flow-website:0.0.3 .circleci/images/website
docker push flowtype/flow-website:0.0.3
```

https://hub.docker.com/layers/flowtype/flow-website/0.0.3/images/sha256-7df0a4a0bf941d559c9c9a479560b06b9833a93c3faa4774af7fcd3328ca76e3?context=explore

Reviewed By: panagosg7

Differential Revision: D21725708

fbshipit-source-id: 38c632eddfab0d535832d967b6dd4ec58dc23d7f

nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow