Spree master is now 2.4.0.rc3
Should be in singular.
Make user confirmation configurable.

fixes #232
Update route in spec to reflect https://github.com/spree/spree/commit/36c5dc9bb554956a9d12ba171c21fd89e740b838
Update build matrix.
Merge pull request #230 from futhr/feature/rc3

Spree master is now rc3.