Zulip Server 1.9.2 maintenance release

[Tim Abbott]

Zulip Server 1.9.2 has been released.  The purpose of this release is to migrate Zulip's Google Authentication to replace a deprecated Google+ API; if you aren't using Google Authentication, you don't need to upgrade.  

Servers using Google authentication should upgrade as soon as possible to avoid disruption of Google authentication.  While Google will not be removing the API entirely until March, they have announced that they will be making certain API requests fail a small percentage of the time, starting yesterday. 

The details are in our release notes blog post, but the other changes in this release are improvements to the Zulip installation experience (Slack import, etc.) that do not effect existing installations.  

-Tim Abbott