Create base and head branches before running danger

[tomhughes]

Let's have another go at getting danger working shall we...

This avoids the need to path danger, and resolves the problems with not fetching enough history for PRs with many commits, by prefetching the data and creating local danger_base and danger_head branches which are the default names that danger looks for.

[mmd-osm]

Gemfile.lock update seems to be missing in the PR...

[tomhughes]

That should be fixed now...

[mmd-osm]

@nenad-vujicic : this might be a good topic for another rule in Dangerfile. Something like:

gemfile_modified = git.modified_files.include?("Gemfile")
gemfile_lock_modified = git.modified_files.include?("Gemfile.lock")

if gemfile_modified && !gemfile_lock_modified
  warn("Gemfile was updated, but Gemfile.lock wasn't updated. Usually, when Gemfile is updated, you should run `bundle install`.")
end

[nenad-vujicic]

This works perfectly on my side. I tested it by applying patches on my personal fork, forking my personal fork from another account and creating 2 PRs (one with 20 commits - worked perfectly, one with changed only Gemfile - worked perfectly again by generating appropriate label) for which new workflow worked fine.

Thanks!

[gravitystorm]

Merged, thanks!