remove `isDevelopingAddon` from index.js
remove `isDevelopingAddon` from index.js

martndemus/ember-cli-fake-server,201-created/ember-cli-fake-server,201-created/ember-cli-fake-server,jakehow/ember-cli-fake-server,balinterdi/ember-cli-fake-server,balinterdi/ember-cli-fake-server,martndemus/ember-cli-fake-server,jakehow/ember-cli-fake-server