Make test organization names more unique

The addition of a uniqueness validation on Organization#name is causing
a lot of random failures; the Organization factory uses a Faker value,
but appears to be producing repetitive results, so I've added a
FactoryGirl sequence to ensure uniqueness.

spec/factories/organizations.rb

@@ -1,6 +1,6 @@
 FactoryGirl.define do
   factory :organization do
-    name { Faker::Company.name }
+    sequence(:name) { |n| "#{Faker::Company.name} #{n}" }
     description { Faker::Lorem.paragraph }
 
     # after(:create) do |organization|