Add test_after_commit gem

Fixes the indexing of papers when running the tests since they are wrapped in a transaction. 

see http://www.justinweiss.com/articles/a-couple-callback-gotchas-and-a-rails-5-fix/

Gemfile

@@ -59,6 +59,7 @@ group :test do
   gem 'shoulda-matchers', '~> 3.1'
   gem 'faker'
   gem 'simplecov', require: false
+  gem 'test_after_commit' # TODO remove when moving to rails 5
 end
 
 # Use ActiveModel has_secure_password

Gemfile.lock

@@ -248,6 +248,8 @@ GEM
     sqlite3 (1.3.10)
     temple (0.7.5)
     terminal-notifier-guard (1.6.4)
+    test_after_commit (0.4.2)
+      activerecord (>= 3.2)
     thor (0.19.1)
     thread_safe (0.3.5)
     tilt (1.4.1)
@@ -299,6 +301,7 @@ DEPENDENCIES
   spring-commands-rspec
   sqlite3
   terminal-notifier-guard
+  test_after_commit
   turbolinks
   uglifier
   validate_url