Add two new keys to the `online_editor` property in the `config.json` files: (#384)
Add two new keys to the `online_editor` property in the `config.json` files: (#384)

1. `ace_editor_language`: the language identifier for the Ace editor that is used to edit code on the website
2. `highlightjs_language`: the language identifier for Highlight.js which is used to highlight code on the website
exercism/xjulia