Elm 0.18 compatibility

[spookylukey]

Fixes for Elm 0.18, plus updates for latest elm-test.

[vanwagonet]

I merged the elm-format commit. Could you rebase, and take a look at the .travis.yml?

I haven't done anything in elm for a long while, and am not sure what the best way to do CI is.

[spookylukey]

@vanwagonet I'll have a look, one of them is the code linter complaining it seems, I'm not sure about the other.

[spookylukey]

@vanwagonet OK, progress here.

We are now seeing failures only on 'stable' Node (v10.9.0), which is what I also get locally, while lts (v8.11.4) passes.

My guesses are regressions in Intl support in Node, or possibly these are real bugs in elm-intl that have been uncovered by better Intl support in Node, I don't have time to look into these at the moment.

[vanwagonet]

I think there are actual regressions in Node v10 Intl support. nodejs/node#22156

I think this is good to merge.

[srl295]

@vanwagonet ^ regression fixed in nodejs/node#23764

[vanwagonet]

Thanks @srl295!