Wrong Reactionary dependence

exports/atom.coffee requires package `reactionary` while atom only has `reactionary-atom-fork` as a dependence (https://github.com/atom/atom/blob/master/package.json#L53). Should require `reactionary-atom-fork` instead.

It's clear that `Reactionary` will soon be omitted from atom's module exports, but as long as fallbacks are provided, the `reactionary` package reference should be corrected. :)
Updated deprecation msg to reactionary-atom-fork
Merge pull request #4286 from m0x72/patch-1

Wrong Reactionary dependence