Please read for an updated status on RailsCasts:
Learn more or hide this
GitHub User: danielmyasnikov
There is a solution on how to resolve dependency.
So basically, you have to go to gemspec of metric_fu and change it from 0.3.0 to 0.6.4
Google it there is a better explanation of what I tried it roughly explain.
It is a great gem and hope you will enjoy reports provided by it.