Merge pull request #63 from pbechu/barcode-validator

check_validity! for BarcodeValidator
3.0.1 should have been 3.1.0. :bomb:

I thought I was avoiding me some headaches but I failed: 3.0.1 should
have been 3.1.0. I probably broke some apps so I owe you an apology.

Upgrading to ActiveValidators 3 should be done like this:

1. Specify the v3 version like that:

    gem 'activevalidators', '~> 3.0.0'

2. Make sure you use `ActiveValidators.activate`
3. Run your test suite
4. Loosen up the dependency like that:

    gem 'activevalidators', '~> 3.0'

Thanks @richardkmichael for pointing this problem out and helping me
find a solution.
Cryptographically sign ActiveValidators

Starting with ActiveValidators 3.1.2, the gems will be signed. Please
refer to the README for instructions on how to do it.