Add a better error when the user has a version of Nix that is too old.  Closes #1.
Add a better error when the user has a version of Nix that is too old.  Closes #1.

paldepind/try-reflex,unisonweb/unison-dependencies,ryantrinkle/try-reflex,ocharles/try-reflex,ajnsit/reflex-platform,reflex-frp/reflex-platform,reflex-frp/reflex-platform,reflex-frp/reflex-platform,meiersi/try-blaze-react