[BUG] Specs mentioned in How to track algorithmic error using PennyLane demo

[DSGuala]

Issue description

The How to track algorithmic error using PennyLane demo mentions qml.specs even though that is no longer used for algorithmic error estimation:

• Expected behavior:

The demo mentions qml.algo_error

[josh146]

Thanks @DSGuala for catching this! Would you be able to make the correction quickly?