Require 'active_support' first

I was hitting an [error](https://travis-ci.org/RoboticCheese/clamav-chef/builds/36737386#L184) in an application that uses this gem by way of droplet_kit:

```
NameError: uninitialized constant ActiveSupport::Autoload
```

and was led to https://github.com/rails/rails/issues/14664. Adding the suggested extra `require` seems to fix the issue.