message: return true if no error occurs on deleting lecture and update course
diff: @@ -112,6 +112,8 @@ export class LectureController {
  * @api {delete} /api/lecture/:id Delete lecture
  * @apiName DeleteLecture
  * @apiGroup Lecture
  + * @apiPermission teacher
  + * @apiPermission admin
  *
  * @apiParam {String} id Lecture ID.
  *
  @@ -125,15 +127,17 @@ export class LectureController {
  @Authorized(['teacher', 'admin'])
  @Delete('/:id')
  async deleteLecture(@Param('id') id: string, @CurrentUser() currentUser: IUser) {
  - const course = await Course.findOne({where: {lectures: id}});
  + const course = await Course.findOne({ lectures: id});
  if (!course) {
  throw new NotFoundError();
  }
  - if (!course.checkPrivileges(currentUser).userCanEditCourse()) {
  + if (!course.checkPrivileges(currentUser).userCanEditCourse) {
  throw new ForbiddenError();
  }
  - const success = await course.update({}, {$pull: {lectures: id}});
  + await course.update({}, {$pull: {lectures: id}});
  +
  + await Lecture.findByIdAndRemove(id);
  - return Lecture.findByIdAndRemove(id) && success;
  + return {result: true};
  }
  }
  