Bundle update rspec-rails

We need to this to support testing Sidekiq jobs inline, see
rails/rails#37270 and
rspec/rspec-rails#2242 for more information.

Gemfile

@@ -45,7 +45,7 @@ group :development, :test do
   gem "rack", ">= 2.0.6"
   gem "rails-controller-testing"
   gem "rspec-its"
-  gem "rspec-rails"
+  gem "rspec-rails", "4.0.0.rc1"
   gem "rubocop-govuk", "~> 3.3"
   gem "shoulda-matchers"
   gem "simplecov", require: false

Gemfile.lock

@@ -327,14 +327,14 @@ GEM
     rspec-mocks (3.9.1)
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.9.0)
-    rspec-rails (3.9.1)
-      actionpack (>= 3.0)
-      activesupport (>= 3.0)
-      railties (>= 3.0)
-      rspec-core (~> 3.9.0)
-      rspec-expectations (~> 3.9.0)
-      rspec-mocks (~> 3.9.0)
-      rspec-support (~> 3.9.0)
+    rspec-rails (4.0.0.rc1)
+      actionpack (>= 4.2)
+      activesupport (>= 4.2)
+      railties (>= 4.2)
+      rspec-core (~> 3.9)
+      rspec-expectations (~> 3.9)
+      rspec-mocks (~> 3.9)
+      rspec-support (~> 3.9)
     rspec-support (3.9.2)
     rubocop (0.80.1)
       jaro_winkler (~> 1.5.1)
@@ -465,7 +465,7 @@ DEPENDENCIES
   rails-controller-testing
   rails-erd
   rspec-its
-  rspec-rails
+  rspec-rails (= 4.0.0.rc1)
   rubocop-govuk (~> 3.3)
   ruby-progressbar
   scenic