Remove required html from update template

[gaijinsan]

Attempting to update a template's name requires the html of the template to be included as well.

Mailchimp's page here (https://developer.mailchimp.com/documentation/mailchimp/reference/templates/#%20) implies that the param is required because of the asterisk. This seems to be a copy/paste oversight from the create template documentation.

If the html required code in templates.py is commented out, a name update is successful.

[stephenross]

Sorry for the almost year-old response. Please contact MailChimp support about the documentation error, and if they indicate that the documentation is indeed incorrect, let us know and you can submit a PR with the change you mentioned for merging.