Fix #716 crash with reset flag

Adds a `rules` key when the `--reset` flag is used so that `Object.keys(config.rules)` doesn't fail. There were multiple similar issues where the presence of `rules` was assumed, so changing it once was the most straightforward solution.

This issue wasn't picked up by the tests because the tests saw the .eslintrc in the project root, which gave the config a `rules` key and masked the error.