Have Resource#inherited call through to Class#inherited

[mtrudel]

The Resource class does not call through to Class#inherited. As a result the various ActiveSupport functions for interrogating a resource's subclasses (Resource.subclasses, Resource.descendents and the like) return empty result sets. This is because Resources override the inherited function but do not call through to their superclass. This PR adds the super call to enable this.

Fixes #1337

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Bug fixes and Changes to Core Features:

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Test Plan:

Reviewer Checklist:

• Maintains compliance with JSON:API
• Adequate test coverage exists to prevent regressions

[mtrudel]

Test failure seems to be isolated to a single CI matrix entry & looks unrelated to the changes in this PR - see https://travis-ci.org/github/cerebris/jsonapi-resources/jobs/745702545

[utilityboy]

@lgebhardt, was there a specific reason why the call to super in this PR was excluded? We've tested on our fork and things appear to work as expected, but wanted to double-check in case there is any nuance we're missing. Many thanks!

[bf4]

👍 this is really just a best practice. I don't think there's a test needed