[DRE-maint] Bug#918402: open-build-service FTBFS with rails 5.2.0

[Adrian Bunk]

Source: open-build-service
Version: 2.7.4-3
Severity: serious
Tags: ftbfs

https://tests.reproducible-builds.org/debian/rb-pkg/unstable/amd64/open-build-service.html

...
/usr/lib/ruby/vendor_ruby/bundler/resolver.rb:289:in `block in verify_gemfile_dependencies_are_found!': Could not find gem 'rails (~> 4.2.2)' in any of the gem sources listed in your Gemfile. (Bundler::GemNotFound)
...