Do not ignore if route is a constraint

Hi,

I found out that routes that are defined within constraint block don't get displayed in missing definitions because of [this line](https://github.com/felipeelias/api_taster/pull/new/fix-routes-with-constraints#L0L38).

Since the #discover_rack_app method looks inside the constraint for the rack app, I think this line is not necessary.

Let me know how can I improve this P.R. with tests.