I have resolved the problem my myself.
My mistake was not to looking carefully enough on rake routes. In 3rd level of nested routes one of element was member element, and one was resource. The name of parameters were different - for member element it was just a "name", where for resource it is "repo_name". In constraints I was setting it for "repo_name" - so the "name" was not accepting the dots.
A bit automagical thing is that when I changed the constraints from { repo_name: /.+/ } to { name: /.+/ }, the both the name and repo_name parameters are accepting the dots.