Add Cirrus CI support

[RDIL]

The real challenge is to see if fkorotkov and his mighty search bar find this PR ;)

If you do see this Fedor, hey 👋

[orta]

Looks good to me - but without this sort of documentation people won't know how to use it -

danger-js/source/ci_source/providers/Travis.ts

Lines 3 to 56 in 2803ede

	/**
	* ### CI Setup
	*
	* <!-- JS --!>
	* You need to edit your `.travis.yml` to include `[run_command]`. If you already have
	* a `script:` section then we recommend adding this command at the end of the script step: `- [run_command]`.
	*
	* Otherwise, add a `before_script` step to the root of the `.travis.yml` with `[run_command]`
	*
	* ```ruby
	* before_script:
	* - yarn danger ci
	* ```
	*
	* Adding this to your `.travis.yml` allows Danger to fail your build, both on the TravisCI website and within your Pull Request.
	* With that set up, you can edit your job to add `[run_command]` at the build action.
	* <!-- !JS --!>
	* <!-- Swift --!>
	*
	* Here's an example of the optimal travis setup, handling caching correctly:
	*
	* ```yml
	* os: osx
	* osx_image: xcode10.1
	*
	* cache:
	* directories:
	* # General SwiftPM
	* # Danger Swift plugins, like Yams
	* - .build
	* - ~/.danger-swift
	*
	* install:
	* # Grab the latest Danger JS from npm
	* - npm install -g danger
	* # Compile the Danger runtime
	* - swift build
	*
	* script:
	* # Run the Dangerfile.swift
	* - swift run danger-swift ci
	* # Test my app...
	* - [your other commands]
	* ```
	*
	* <!-- !Swift --!>
	*
	* ### Token Setup
	*
	* You need to add the `DANGER_GITHUB_API_TOKEN` environment variable, to do this,
	* go to your repo's settings, which should look like: `https://travis-ci.org/[user]/[repo]/settings`.
	*
	* If you have an open source project, you should ensure "Display value in build log" enabled, so that PRs from forks work.
	*/

Any chance you can add that?

[RDIL]

Please re review @orta

[orta]

Ace 👍

[peril-staging]

Thanks for the PR @RDIL.

This PR has been shipped in v9.2.5 - CHANGELOG.