acai-cli: add --reverse flag

[MartinHelmut]

Like already mentioned in #2 there should be a flag to reverse the output from lowest to highest (--reverse / -R). This could be used like:

$ acai --reverse

That results in the following example output:

✔ Found 13 fix(es) in 11 file(s) (in 0.07s).

Show 11 hot spots:
  Score                     File
  0.000039293793783420496 - packages/acai/README.md
  0.004268992522721866    - CONTRIBUTING.md
  0.02554274739945699     - packages/acai-cli/package.json
  0.0514120555342579      - packages/acai-cli/README.md
  0.09074481528078868     - package-lock.json
  0.09074481528078868     - packages/acai-cli/__tests__/bin.test.js
  0.09074481528078868     - packages/acai-cli/bin.js
  0.09171815638547412     - packages/acai-cli/src/formatter/human.js
  0.2766621734649931      - packages/acai-cli/src/argv.js
  0.32063790545957743     - packages/acai-cli/src/cli.js
  1                       - packages/acai/src/adapter/git.js

This enables the user to get files with a very low bug density in the recent past.