Use RSpec 4 pre-release

RSpec 4 will eventually be released. Since we're checking its style, why
don't we use it. This will help a bit to test it out.

Author: pirj

.rspec

@@ -1,3 +1,2 @@
 --require spec_helper
---color
 --format documentation

Gemfile

@@ -6,7 +6,9 @@ gemspec
 
 gem 'rack'
 gem 'rake'
-gem 'rspec', '>= 3.4'
+%w[rspec rspec-core rspec-expectations rspec-mocks rspec-support].each do |repo|
+  gem repo, github: "rspec/#{repo}", branch: '4-0-dev'
+end
 gem 'rubocop-performance', '~> 1.7'
 gem 'rubocop-rake', '~> 0.6'
 gem 'yard'

spec/smoke_tests/weird_rspec_spec.rb

@@ -86,7 +86,7 @@
   end
 
   it_behaves_like :something
-  it_should_behave_like :something
+  # it_should_behave_like :something
 
   it_behaves_like :something do
     let(:foo) { 'bar' }

spec/spec_helper.rb

@@ -24,11 +24,7 @@ module SpecHelper
   config.order = :random
 
   # Run focused tests with `fdescribe`, `fit`, `:focus` etc.
-  config.filter_run focus: true
-  config.run_all_when_everything_filtered = true
-
-  # Forbid RSpec from monkey patching any of our objects
-  config.disable_monkey_patching!
+  config.filter_run_when_matching :focus
 
   # We should address configuration warnings when we upgrade
   config.raise_errors_for_deprecations!