change default auth url

[argovaerts]

https://github.com/kylewm/flask-micropub/blob/897c75848c441758d61c11e36c02ae9c1f786950/flask_micropub.py#L24

Change too DEFAULT_AUTH_URL = 'https://indielogin.com/auth' as indieauth.com is being deprecated.

[martymcguire]

note that indielogin.com is not yet open to the public as of 2018-05-22 at least.

developers may be able to automate registration at some point

[tswast]

Looks like it’s open now. https://indielogin.com

[martymcguire]

@tswast: while the site is available for testing your own site's configuration, it is not currently open to client apps like those that would use flask-micropub.

@aaronpk can answer this definitively.