Fix core specs.
Used transpec to update backend specs to rspec 3.
Convert specs to RSpec 3.1.7 syntax with Transpec

This conversion is done by Transpec 2.3.7 with the following command:
    transpec -s

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

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

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

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

* 17 conversions
    from: Klass.any_instance.stub(:message => value)
      to: allow_any_instance_of(Klass).to receive_messages(:message => value)

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

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

* 10 conversions
    from: obj.stub(:message => value)
      to: allow(obj).to receive_messages(:message => value)

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

* 8 conversions
    from: obj.stub_chain(:message1, :message2)
      to: allow(obj).to receive_message_chain(:message1, :message2)

* 7 conversions
    from: =~ /pattern/
      to: match(/pattern/)

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

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

* 3 conversions
    from: > expected
      to: be > expected

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

* 1 conversion
    from: =~ [1, 2]
      to: match_array([1, 2])

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

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

For more details: https://github.com/yujinakayama/transpec#supported-conversions
Fix remaining deprecations in helpers.