[WIP] Configure Danger

[AliSoftware]

First attempt at configuring Danger for this repository

Note: Once this works, we might want to migrate the installation of the xcpretty gem into the Gemfile as well — now that we have one to include Danger — and alter the .travis.yml accordingly.

[SwiftGen-Eve]

	1 Error
🚫	Please include a CHANGELOG entry. You can find it at CHANGELOG.md.

	1 Warning
⚠️	PR is classed as Work in Progress

Note: we use the following format for CHANGELOG entries:

 * [WIP] Configure Danger.  
   [#12](https://github.com/SwiftGen/templates/pull/12)
   [@AliSoftware](https://github.com/AliSoftware)

💡 Don't forget to use 2 spaces after the full stop at the end of the line describing your changes.

Generated by 🚫 Danger

[djbe]

Need to add DANGER_GITHUB_API_TOKEN to the circleci configuration.

[AliSoftware]

Done!

btw looking at the rake compile:output log files used:

• Their named is only used based on the context being used but not the subcommand. This results in e.g. output_compile_default_context_empty_raw.log to be used as a log file for storyboards + strings + colors etc, each overriding the previous one
• it could be worth making it possible to group/organize them in a folder, like output_compile/strings/default_context_empty_raw.log

Basically, in Utils.run, maybe the subtask parameter should add a _ in the file path but a / instead? (even if we might have to mkdir -p the directory first in those cases to ensure it exists)

[djbe]

Will look into it. Also saw something reaaaally interesting on Slack today:
https://github.com/orta/danger-junit
Integrates failed tests into danger.