High CPU load without refresh

[RobinJadoul]

When refresh is left disabled, flask_moment_render is constantly called by the setInterval call.
This is due to the following sequence of events:

• At https://github.com/miguelgrinberg/Flask-Moment/blob/main/src/flask_moment/__init__.py#L171, the data-refresh attribute is set to "{}".format(int(False)) == "0"
• In the browser, the check at https://github.com/miguelgrinberg/Flask-Moment/blob/main/src/flask_moment/__init__.py#L105 succeeds, since "0" is a truthy value
• This results in setInterval getting the argument "0" as interval argument, which the browser presumably interprets as "as often as possible"; for every moment on the page