Update a spec to work in rubies that don't support required kwargs

Author: bryanp

spec/rspec/mocks/and_call_original_spec.rb

@@ -188,7 +188,7 @@ class << self
     if RSpec::Support::RubyFeatures.kw_args_supported?
       binding.eval(<<-CODE, __FILE__, __LINE__)
       it "works for methods that accept keyword arguments" do
-        def instance.foo(bar:); bar; end
+        def instance.foo(bar: nil); bar; end
         expect(instance).to receive(:foo).and_call_original
         expect(instance.foo(bar: "baz")).to eq("baz")
       end