fix bad import

tracim/views/core_api/workspace_controller.py

 from tracim.models.context_models import UserRoleWorkspaceInContext
 from tracim.models.context_models import ContentInContext
 from tracim.exceptions import EmptyLabelNotAllowed
-from tracim.exceptions import ContentNotFoundFound
+from tracim.exceptions import ContentNotFound
 from tracim.exceptions import WorkspacesDoNotMatch
 from tracim.exceptions import ParentNotFound
 from tracim.views.controllers import Controller