[FEATURE] Exclude Dependabot PRs

[GuilleLeopold]

[diego-suarez]

at: https://github.com/rootstrap/pull_requests_to_slack/blob/8bf1271077fce5c091ef7bf3df280f412c149d2d/app/services/slack_notification_service.rb#L34 it checks for pr.blacklisted? defined as: https://github.com/rootstrap/pull_requests_to_slack/blob/8bf1271077fce5c091ef7bf3df280f412c149d2d/app/services/pull_request.rb#L38

It checks for an existing User on the database, with the username and the attribute blacklisted: true

Can't that be used to exclude dependabot PRs? (creating a row on users table with github_name: 'dependabot', blackslited: true?

[megatux]

I guess it should. I created a PR, #89, to prove the comment above