PullReview: disable dups & docs checks on specs

@moonglum, as suggested in #133 :smile: 
Here an example of config file to disable duplications and doc checks on tests.

To enable reviewing of PullRequests from forks (once the project is added to PullReview):
* Go to the webhooks settings of your repo https://github.com/triAGENS/ashikawa-core/settings/hooks
* Edit the hook https://www.pullreview.com/api/push/github
* In section "Which events would you like to trigger this webhook?" / "Let me select individual events." select "Pull Request" in addition the already selected "Push"
* Click "Update Webhook"

If you're interested, I can submit a commit to check that your modifications on a branch are covered by a test.