Fix event.json path in new GitHub Actions
Fix event.json path in new GitHub Actions

When using danger through `node_modules` during new actions run i.e `run: yarn danger ci` as opposed to `uses: danger/danger-js` path to `event.json` file is different. Path to this file exists on `GITHUB_EVENT_PATH` env variable.

Further discussion happened here: https://spectrum.chat/danger/general/does-danger-support-new-github-actions~e19e146a-c155-4e29-9b2b-d2ad9c3da3f0
danger/danger-js,danger/danger-js,danger/danger-js,danger/danger-js