Use newer mail_room to get `require_relative` support

Gemfile

@@ -333,7 +333,7 @@ gem 'newrelic_rpm', '~> 3.16'
 
 gem 'octokit', '~> 4.6.2'
 
-gem 'mail_room', '~> 0.9.0'
+gem 'mail_room', '~> 0.9.1'
 
 gem 'email_reply_trimmer', '~> 0.1'
 gem 'html2text'

Gemfile.lock

@@ -409,7 +409,7 @@ GEM
       nokogiri (>= 1.5.9)
     mail (2.6.4)
       mime-types (>= 1.16, < 4)
-    mail_room (0.9.0)
+    mail_room (0.9.1)
     memoist (0.15.0)
     method_source (0.8.2)
     mime-types (2.99.3)
@@ -912,7 +912,7 @@ DEPENDENCIES
   license_finder (~> 2.1.0)
   licensee (~> 8.0.0)
   loofah (~> 2.0.3)
-  mail_room (~> 0.9.0)
+  mail_room (~> 0.9.1)
   method_source (~> 0.8)
   minitest (~> 5.7.0)
   mousetrap-rails (~> 1.4.6)

config/mail_room.yml

@@ -1,9 +1,6 @@
-# If you change this file in a Merge Request, please also create
-# a Merge Request on https://gitlab.com/gitlab-org/omnibus-gitlab/merge_requests
-#
 :mailboxes:
   <%
-    require_relative "lib/gitlab/mail_room" unless defined?(Gitlab::MailRoom)
+    require_relative "../lib/gitlab/mail_room" unless defined?(Gitlab::MailRoom)
     config = Gitlab::MailRoom.config
 
     if Gitlab::MailRoom.enabled?

spec/config/mail_room_spec.rb

@@ -8,7 +8,7 @@ describe 'mail_room.yml' do
 
   context 'when incoming email is disabled' do
     before do
-      ENV['MAIL_ROOM_GITLAB_CONFIG_FILE'] = Rails.root.join('spec/fixtures/mail_room_disabled.yml').to_s
+      ENV['MAIL_ROOM_GITLAB_CONFIG_FILE'] = Rails.root.join('spec/fixtures/config/mail_room_disabled.yml').to_s
       Gitlab::MailRoom.reset_config!
     end
 
@@ -26,7 +26,7 @@ describe 'mail_room.yml' do
     let(:gitlab_redis) { Gitlab::Redis.new(Rails.env) }
 
     before do
-      ENV['MAIL_ROOM_GITLAB_CONFIG_FILE'] = Rails.root.join('spec/fixtures/mail_room_enabled.yml').to_s
+      ENV['MAIL_ROOM_GITLAB_CONFIG_FILE'] = Rails.root.join('spec/fixtures/config/mail_room_enabled.yml').to_s
       Gitlab::MailRoom.reset_config!
     end