Specification of ActiveModel Version During Testing

[fny]

The following adds the ability to test the validator against various versions of ActiveModel:

rake test # defaults to '~> 3'

# Specify a rails version with the pessimistic version operator
ACTIVE_MODEL=4.0.0 rake test # '~> 4.0.0'

 # Run tests against master branch on GitHub
ACTIVE_MODEL=master rake test

Travis configs have been updated to test for multiple Rails versions as well

[fny]

The only outstanding issue is Rails v4 with Ruby 1.9.2:

Gem::InstallError: activesupport requires Ruby version >= 1.9.3.
An error occurred while installing activesupport (4.0.0), and Bundler cannot

See the Travis CI build for more info.

[spider-network]

+1

[txus]

Thanks!