Add missing rails_server dev dependencies

Author: glebm

bootstrap.gemspec

@@ -27,6 +27,8 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'capybara', '>= 2.6.0'
   s.add_development_dependency 'cuprite'
   # Dummy Rails app dependencies
+  s.add_development_dependency 'dartsass-sprockets'
+  s.add_development_dependency 'railties'
   s.add_development_dependency 'actionpack', '>= 4.1.5'
   s.add_development_dependency 'activesupport', '>= 4.1.5'
   s.add_development_dependency 'json', '>= 1.8.1'