Fix to allow lein test to to run successfully

Fixed core.clj and associated deps in project to allow (run-cukes) to execute from repl and 'lein test' to succeed.
This change breaks the build (see [Travis](https://travis-ci.org/cucumber/cucumber-jvm/builds/42976734)). Instead the feature description should be changed from "The last 'Then' ... is failing", to something like "to provoke a failure change the last 'Then' form 'meh' to 'happy'".