Upgrade to 0.19

[mattjbray]

Work is under way at https://github.com/mattjbray/servant-elm/compare/019-tostring

[domenkozar]

There is a PR up: #45

[szg251]

I just noticed that the NoRedInk fork https://github.com/NoRedInk/servant-elm seems to be more active, haven't tried it yet but it should work with Elm 0.19. They also have a fork of elm-export which is the main dependency of this package.

[andys8]

It was updated. https://github.com/haskell-servant/servant-elm/blob/master/CHANGELOG.md#0600
#49

This ticket can be issue.