Typo fix s/BooleanInput/NullableBooleanInput/
Typo fix s/BooleanInput/NullableBooleanInput/

As requested by @Kmaschta at https://github.com/marmelab/admin-on-rest/pull/52#discussion_r81341146
marmelab/admin-on-rest,matteolc/admin-on-rest,matteolc/admin-on-rest,marmelab/admin-on-rest