change "execute" into "jupyter-execute"

docs/source/rest_of_readme.rst

docs/source/tutorial/tutorial.AverageLearner.rst

docs/source/tutorial/tutorial.BalancingLearner.rst

docs/source/tutorial/tutorial.DataSaver.rst

docs/source/tutorial/tutorial.IntegratorLearner.rst

docs/source/tutorial/tutorial.Learner1D.rst

docs/source/tutorial/tutorial.Learner2D.rst

docs/source/tutorial/tutorial.LearnerND.rst

docs/source/tutorial/tutorial.SKOptLearner.rst

docs/source/tutorial/tutorial.advanced-topics.rst

docs/source/tutorial/tutorial.custom_loss.rst