Pleaes support latest configatron

[austvik]

I get error message when using cover_me because it doesn't support configatron v3 series.

The first issue I hit is that "store" is now a method on the config object and therefore a unfortunate name for a configuration value. Then (when I change name from "store" to "file_store"), I hit problems setting default values.

$ bundle update configatron
before building/running tests with coverage should reproduce the problem.