Update Git on prod

[techtonik]

This is required to fix Edit button on annotated tags
#3441 (reverted fix)

[ericholscher]

I wish this is as easy as it was to update git in our production instances. Our builders are currently running 14.04, so "update git in prod" actually means "fully re-deploy an entire stack of servers". We're going to be transitioning away from Rackspace soon, so that upgrade will take place as part of our server migrations.

[techtonik]

@ericholscher from https://docs.readthedocs.io/en/latest/development/buildenvironments.html it looks like those builders are Docker images, so changing them to 16.04 should be easy.

[ericholscher]

Git is currently run outside of docker in some cases, for reasons :)

[techtonik]

@ericholscher are there any security reasons to keep the workflow undocumented? =)

[ericholscher]

Just lack of time.

[humitos]

Thanks!

I think we can merge this already.

Servers where upgraded to 16.04 and they are running git 2.7.4 at the moment.

[stsewd]

I'm fixing the edit button problem using gitpython on #4052

[ericholscher]

Will go ahead and merge this, as I believe our git is upgraded in production.