Outdated link to API reference in README

[PixelPartner]

Dear @ianmackenzie
I suggest to change the API Ref in README to point to /latest/ instead of the outdated /1.0.0/

[ianmackenzie]

Oops, thanks for the heads-up! I see that there has just recently been released an elm-review package that checks for this exact error, so maybe I should try it out =)