In Rails 5.0 `assert_template` and `assigns()` have been extracted to
the `rails-controller-testing` gem.
https://github.com/rails/rails/pull/20138/files
This commit adds this gem for rails5.
1. Synchronize used version of `parser` gem for both versions of rails: 4 and 5.
2. Fix broken CI pipelines for rails5 branches.
The 2.5.0.4 version is removed from rubygems, so it's skipped.
https://github.com/whitequark/parser/issues/478
blackst0ne