Fail tests for dirty tracking type casting

@byroot @qq99

These tests show this failure:

```
[12] pry> shop.password_enabled?
=> false
[13] pry> shop.password_enabled = "false"
=> "false"
[14] pry> shop.password_enabled?
=> false
[15] pry> shop.password_enabled_changed?
=> true
```
It installed newest rspec `3.0.x` which failed on `is_true` needing to be `is_truthy` deprecations.