Resolve issue with resolving configuration

[Bouke]

See #231 for additional information. Beware that I've removed the following config resolvers:

(app && app.project.config(app.env)['SemanticUI'])
|| (app && app.project.config(app.env)['semantic-ui-ember'])

I don't know what these do and where they get their config from. The change proposed in this PR reflects the actual documentation and has been tested on ember-cli 3.0.

[codecov-io]

Codecov Report

Merging #232 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #232   +/-   ##
=======================================
  Coverage   81.78%   81.78%           
=======================================
  Files          14       14           
  Lines         516      516           
  Branches       24       24           
=======================================
  Hits          422      422           
  Misses         94       94

Impacted Files	Coverage Δ
index.js	75.88% <100%> (ø)	⬆️

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[Bouke]

When do you expect to create a new release? Now that the configuration issue has been resolved, it would be great to start using an official release.