Seems to be broken on current ubuntu lts.

There are two issues with installation.
1. The elm download location has changed.
2. elm 0.18 requires downgrading to node v10
```
npm ERR! Downloading Elm binaries from https://dl.bintray.com/elmlang/elm-platform/0.18.0/linux-x64.tar.gz                             
npm ERR! Error decompressing linux-x64.tar.gz Error: incorrect header check         
```