[Certbot-dev] Certbot 1.15.0 Release

[Brad Warren]

We just released Certbot 1.15.0. There were no significant user facing changes in this release. Instead, most of the changes were internal refactoring following up on us dropping Python 2 support and preparing to add more [mypy](http://mypy-lang.org/) type annotations in the hopes of largely eliminating potential type errors from Certbot to make it more reliable.

We should have user facing changes to talk about in our release next month.