Move nixpkgs/github.json to NixOS/nixpkgs
Move nixpkgs/github.json to NixOS/nixpkgs

This means everything is now in Nixpkgs that we need for reflex-platform.

reflex-frp/reflex-platform,reflex-frp/reflex-platform,reflex-frp/reflex-platform,ryantrinkle/try-reflex