Update to Virtus 1.0.3

Update to Virtus 1.0.3.
Update to Rspec 3.
Update to Ruby 2.1.2.
Can you slacken off these dependencies please?

```ruby
gem.add_dependency "rspec", ">= 3.0"
gem.add_dependency "virtus", ">= 1.0"
```

This will allow the gem to be most flexible when upgrades come out.