Bump alpine 3.9.0 to 3.9.2

[tremaineeto]

Fixes #495

Alpine 3.9.2 was released today (3/4/19). I looked at some previous commits that did a similar version bump, but I wasn't sure if this is all that needed to be done (or if we need to wait for something else) or if there is more necessary. Wanted to take a stab at it but it's my first commit here and wasn't sure the exact procedures/testing processes.

[oliv3r]

@tianon @gliderbot can we get some feedback on this bump? before we have to make it a 3.9.3 bump? :)

[tianon]

The actual artifacts for the alpine official image have moved over to https://github.com/alpinelinux/docker-alpine, and looking at https://github.com/alpinelinux/docker-alpine/blob/v3.9/VERSION, it already has this bump (as can be seen by the availability of the alpine:3.9.2 tag, which is also new with the introduction of that repository).

[oliv3r]

So I take it all the open PR's here are probably then just going to go stale/closed? Also that would mean that the docker hub needs some updating?

[mtgto]

latest Alpine 3.9 is now 3.9.4!

In test directory, tests about 3.6, 3.7 and 3.8 have same problem in this PR.
It is the reason why CircleCI in my PR #503 is failed.