Update generator to be Rails 4 compliant

The default argument workaround was originally found here: https://github.com/norman/friendly_id/pull/392
Merge pull request #8 from danielgrippi/patch-1

Update generator to be Rails 4 compliant
Remove unused CI builds
Support Rails 4.2
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Always test on latest Ruby patch version
Test on Ruby 2.2
v0.6.4