message: Fix typo. in README.md
diff: ## Why?
  -As Danger uses jest-runtime we need to separate out node_modules for Danger into it's own folder as conflicts [occured](https://github.com/facebook/jest/pull/2532).
  +As Danger uses jest-runtime we need to separate out node_modules for Danger into it's own folder as conflicts [occurred](https://github.com/facebook/jest/pull/2532).
  If you'd like to make changes to the Dangerfile, find an existing PR and copy the URL.
  