Add --no-color option

We're using foreman to run rspec and webpack at the same time within a docker container via a Jenkins job, however, the output is also including the color escape codes causing it to be harder to read.

Would it be possible to add an option to disable color entirely?

```
[36m10:34:03 rspec.1   | [0m  Blacklist
[36m10:34:03 rspec.1   | [0m    redirects to the dashboard
```