Add gem to make tests work with devise callbacks

This is noted in the devise 4.1 release notes: https://github.com/heartcombo/devise/blob/master/CHANGELOG.md#410

Gemfile

@@ -146,6 +146,7 @@ end
 group :test do
   gem 'simplecov', require: false
   gem 'test-prof'
+  gem 'test_after_commit' # needed to test Devise callbacks
   gem 'webmock'
   # See spec/spec_helper.rb for instructions
   # gem 'perftools.rb'

Gemfile.lock

@@ -679,6 +679,8 @@ GEM
     test-prof (0.7.5)
     test-unit (3.3.6)
       power_assert
+    test_after_commit (1.2.2)
+      activerecord (>= 3.2, < 5.0)
     thor (0.20.3)
     thread_safe (0.3.6)
     tilt (1.4.1)
@@ -828,6 +830,7 @@ DEPENDENCIES
   stripe
   test-prof
   test-unit (~> 3.3)
+  test_after_commit
   timecop
   uglifier (>= 1.0.3)
   unicorn