Upgrade tutorial to elm 0.17

[benoitparis]

Learning elm at the moment. This tutorial feels great. If I get pass the hurdles of getting it to compile on 0.17, I'll try to produce a pull request

[ramstein74]

Me want it too :)

[FranklinChen]

Meanwhile, Elm 0.18 has come and gone and Elm is at 0.19 now, so a lot has changed.