Fixed instructions for current rails version

[bluehallu]

minitest task doesn't exist anymore, hook into rake test directly does work.

[shepmaster]

Thanks for your contribution!

CI::Reporter is designed to be used with any Ruby project, not just ones using Rails. As such, the project may create a Rake task with whatever name they choose. Our intent was that the text Rake code that creates a task called :minitest in the README would indicate that.

Do you have a suggestion for how to make this more clear, without picking another static name that will confuse a different person?

[bluehallu]

I see your point, I'd probably explicitly say in the instructions that for rails that's what you need to call as I imagine that's the most popular use case for minitest!