Cap Aruba and ffi to resolve version conflicts

ffi has strict Ruby constraints

aruba:

    Bundler could not find compatible versions for gem "thor":
      In Gemfile:
        aruba (~> 0.14.11) was resolved to 0.14.12, which depends on
          thor (~> 0.19)

        rails (~> 3.1.12) was resolved to 3.1.12, which depends on
          railties (= 3.1.12) was resolved to 3.1.12, which depends on
            thor (~> 0.14.6)

Author: pirj

Gemfile

@@ -30,8 +30,10 @@ end
 
 if RUBY_VERSION < '1.9'
   gem 'ffi', '< 1.9.19' # ffi dropped Ruby 1.8 support in 1.9.19
-else
-  gem 'ffi', '~> 1.9.25'
+elsif RUBY_VERSION < '2.0'
+  gem 'ffi', '< 1.11.0' # ffi dropped Ruby 2.0 support in 1.11.0
+elsif RUBY_VERSION < '2.3'
+  gem 'ffi', '< 1.13.0'
 end
 
 if RUBY_VERSION >= '2.0.0'

rspec-rails.gemspec

@@ -51,6 +51,11 @@ Gem::Specification.new do |s|
   end
 
   s.add_development_dependency 'cucumber', '~> 1.3.5'
-  s.add_development_dependency 'aruba',    '~> 0.14.12'
+  if ENV['RAILS_VERSION'].gsub(/[^\d\.-]/, '').tr('-', '.') < '4.0'
+    # aruba > 0.9 depends on thor ~> 0.19, while railties < 4.0 depend on thor ~> 0.14.6
+    s.add_development_dependency 'aruba', '~> 0.8.1'
+  else
+    s.add_development_dependency 'aruba', '~> 0.14.12'
+  end
   s.add_development_dependency 'ammeter',  '~> 1.1.2'
 end