Mark some examples as pending due to the issue in conversion of #unstub

See: https://github.com/rspec/rspec-mocks/issues/613
Convert specs to RSpec 2.99.0.beta2 syntax with Transpec

This conversion is done by Transpec 1.11.1 with the following command:
    transpec --force --convert stub_with_hash

* 396 conversions
    from: obj.should_receive(:message)
      to: expect(obj).to receive(:message)

* 239 conversions
    from: obj.should
      to: expect(obj).to

* 113 conversions
    from: obj.stub(:message)
      to: allow(obj).to receive(:message)

* 94 conversions
    from: obj.should_not_receive(:message)
      to: expect(obj).not_to receive(:message)

* 86 conversions
    from: == expected
      to: eq(expected)

* 16 conversions
    from: obj.stub(:message => value)
      to: allow(obj).to receive(:message).and_return(value)

* 16 conversions
    from: stub('something')
      to: double('something')

* 15 conversions
    from: be_true
      to: be_truthy

* 15 conversions
    from: obj.stub!(:message)
      to: allow(obj).to receive(:message)

* 13 conversions
    from: mock('something')
      to: double('something')

* 10 conversions
    from: lambda { }.should_not
      to: expect { }.not_to

* 10 conversions
    from: obj.should_not
      to: expect(obj).not_to

* 7 conversions
    from: be_false
      to: be_falsey

* 7 conversions
    from: obj.unstub(:message)
      to: allow(obj).to receive(:message).and_call_original

* 5 conversions
    from: pending
      to: skip

* 4 conversions
    from: lambda { }.should
      to: expect { }.to

* 4 conversions
    from: obj.should_receive(:message).any_number_of_times
      to: allow(obj).to receive(:message)

* 3 conversions
    from: collection.should have(n).items
      to: expect(collection.size).to eq(n)

* 1 conversion
    from: it { should ... }
      to: it { is_expected.to ... }

* 1 conversion
    from: it { should_not ... }
      to: it { is_expected.not_to ... }