Add missing import

web/app/settings/views.py

 from flask import current_app, flash, redirect, render_template, url_for
-from flask_login import current_user, login_required
+from flask_login import current_user, login_required, logout_user
 from . import settings, tasks
 from .forms import (ChangePasswordForm, EditGeneralSettingsForm,
                     EditNotificationSettingsForm)