Move FactoryGirl.lint to rake task

This significantly improves start time of tests. It is also the recommended
way: https://github.com/thoughtbot/factory_girl/blob/master/GETTING_STARTED.md#linting-factories

Read more at: https://github.com/thoughtbot/factory_girl/issues/772

lib/tasks/factory_girl.rake

@@ -0,0 +1,15 @@
+namespace :factory_girl do
+  desc "Verify that all FactoryGirl factories are valid"
+  task lint: :environment do
+    if Rails.env.test?
+      begin
+        DatabaseCleaner.start
+        FactoryGirl.lint
+      ensure
+        DatabaseCleaner.clean
+      end
+    else
+      system("bundle exec rake factory_girl:lint RAILS_ENV='test'")
+    end
+  end
+end

spec/support/factory_girl.rb

@@ -1,7 +0,0 @@
-RSpec.configure do |config|
-
-  config.before(:suite) do
-    FactoryGirl.lint
-  end
-
-end