As Danger uses jest-runtime we need to separate out node_modules for Danger into it's own folder as conflicts occurred.
If you'd like to make changes to the Dangerfile, find an existing PR and copy the URL.
Then run from the Jest root:
cd danger
yarn install
..
node danger/node_modules/.bin/danger pr https://github.com/facebook/jest/pull/2642
And you will get the responses from parsing the Dangerfile.