Cleanup/fix typo in exercise fractures

.patches/exercise-basic/exercise-basic.patch

...ercise-biomineralization/exercise-biomineralization.patch

...hes/exercise-coupling-ff-pm/exercise-coupling-ff-pm.patch

.patches/exercise-dunemodule/exercise-dunemodule.patch

.patches/exercise-fluidsystem/exercise-fluidsystem.patch

.patches/exercise-fractures/exercise-fractures.patch

.patches/exercise-grids/exercise-grids.patch

.patches/exercise-mainfile/exercise-mainfile.patch

.patches/exercise-model/exercise-model.patch

.patches/exercise-properties/exercise-properties.patch

.patches/exercise-runtimeparams/exercise-runtimeparams.patch

exercises/exercise-fractures/main.cc

exercises/solution/exercise-fractures/main.cc