Updating to Rspec 3.1

Convert specs with Transpec, updating gems and adding rspec-activemodel-mocks.

This conversion is done by Transpec 2.3.8 with the following command:
    transpec

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

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

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

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

* 25 conversions
    from: describe 'some feature' { }
      to: describe 'some feature', :type => :feature { }

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

* 18 conversions
    from: Klass.any_instance.stub(:message)
      to: allow_any_instance_of(Klass).to receive(:message)

* 9 conversions
    from: Klass.any_instance.should_receive(:message)
      to: expect_any_instance_of(Klass).to receive(:message)

* 8 conversions
    from: describe 'some controller' { }
      to: describe 'some controller', :type => :controller { }

* 8 conversions
    from: describe 'some model' { }
      to: describe 'some model', :type => :model { }

* 6 conversions
    from: describe 'some view' { }
      to: describe 'some view', :type => :view { }

* 4 conversions
    from: pending 'is an example' { }
      to: skip 'is an example' { }

* 3 conversions
    from: pending
      to: skip

* 1 conversion
    from: be_false
      to: be_falsey

* 1 conversion
    from: be_true
      to: be_truthy

* 1 conversion
    from: describe 'some routing' { }
      to: describe 'some routing', :type => :routing { }

* 1 conversion
    from: expect(obj).to have(n).entries
      to: expect(obj.entries.size).to eq(n)

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

* 1 conversion
    from: lambda { }.should_not
      to: expect { }.not_to

For more details: https://github.com/yujinakayama/transpec#supported-conversions