fixed cost models and problems notebook

docs/notebooks/cost_models.ipynb

docs/notebooks/openmdao_checks.out

docs/notebooks/problems.ipynb

docs/source/basic_examples.rst

docs/source/examples.rst

docs/source/examples_nblinks/bathymetry_nb.nblink

docs/source/examples_nblinks/constraints_nb.nblink

docs/source/examples_nblinks/cost_models_nb.nblink

docs/source/examples_nblinks/drivers_nb.nblink

docs/source/examples_nblinks/exclusion_zones_nb.nblink

docs/source/examples_nblinks/layout_and_loads_nb.nblink

docs/source/examples_nblinks/mongodb_nb.nblink

docs/source/examples_nblinks/problems_nb.nblink

...urce/examples_nblinks/regular_grid_optimization_nb.nblink

docs/source/examples_nblinks/roads_and_cables_nb.nblink

...source/examples_nblinks/wake_steering_and_loads_nb.nblink

docs/source/index.rst