GH issue 3: bring exception message inline with code, :branch _and_ :stage must be defined.
Merge pull request #4 from mydrive/gh3_inconsistent_validation_vs_exception

Issue 3: bring exception message inline with code
Fix test broken by one-line pul request!
Use more modern rspec syntax for lambda
Fix deploy:migrations tagging
Merge pull request #7 from pusewicz/master

Fix tagging on deploy:migrations
Rev for release 0.7.0.