Bumped Elm version requirement to 0.16+

[hughfdjackson]

Recent changes merged into master don't compile with 0.15.x. To
avoid confusion for contributers, this commit requires Elm 0.16+.

The specific PRs that seem to have caused problems for me are #382, which results in a cyclical dependency error, and #375, which complains at duplicate keys in Records for Graphics.Element's width, etc.

[evancz]

Right now nothing will compile with the master branch of elm-compiler. Making this change means we need to do a version bump that will ripple through all the elm repos. elm-package depends on 0.16, etc.

Due to some silly things with cabal, I tend to wait til the last moment to bump all the dependencies.

So given that nothing can be built with the latest compiler anyway, can we wait on this a bit?

[evancz]

Right now nothing will compile with the master branch of elm-compiler. Making this change means we need to do a version bump that will ripple through all the elm repos. elm-package depends on 0.16, etc.

Due to some silly things with cabal, I tend to wait til the last moment to bump all the dependencies.

So given that nothing can be built with the latest compiler anyway, can we wait on this a bit?

[hughfdjackson]

@evancz :) Absolutely. Closing this PR.

[hughfdjackson]

@evancz :) Absolutely. Closing this PR.