dont make AR reflection if rails version is lower than 4.1

Although `rails4.0` is documented to be used with both `rails 4.1` and `rails 4.0`, some issues arise when I try to use it in fresh rails 4.0.5 project.
Assume we've got the basic rails setup with the following models:
```ruby
class User
  acts_as_paranoid
  has_one :dog
end

class Dog
  belongs_to :user
end
```
asking for a `Dog` class in rails console results in the following error:
```ruby
Loading development environment (Rails 4.0.5)
2.1.2 :001 > Dog
NoMethodError: undefined method `values' for #<ActiveRecord::Reflection::AssociationReflection:0x00000003a57730>
from /home/twonegatives/.rvm/gems/ruby-2.1.2@valkyrie/bundler/gems/rails3_acts_as_paranoid-ee21c119f3b4/lib/acts_as_paranoid/associations.rb:13:in `belongs_to_with_deleted'
```

the problem here is that rails 4.0's ActiveRecord::Reflection::AssociationReflection object allows us to ask for its options directly, while rails 4.1 forces to ask for `values` firstly (introduced in [this commit](https://github.com/goodwinproject/rails3_acts_as_paranoid/commit/76f8f9c2a9df055f0eef925d8b691818a5af97f3))

This commit solves an issue by simply checking for rails 4 release version and querying for `values` only if it is required.