Add Node v12 to build matrix

[willmorgan]

What this does:

Adds Node v12 to the build matrix for testing, also adds x86/x64 tests, although not sure if the latter is really needed in 2019 😉

[willmorgan]

Node v12 was made available nearly a month ago, but it isn't yet on AppVeyor. Shame.

appveyor/ci#2921

I'll rework.

[dhensby]

By the looks of things we are only running tests against LTS versions, but v12 is not LTS (yet) so do we want to add it when we don't test any other non-LTS version and appveyor doesn't support it?

[willmorgan]

v12 is not LTS (yet) so do we want to add it when we don't test any other non-LTS version and appveyor doesn't support it?

Odd numbered versions of Node won't ever make it to LTS whereas even numbers will.

Node releases versions destined to be LTS a few months before to get them completely stable before designating them as the LTS version.

https://nodejs.org/en/about/releases/

I think it's worth putting this in. Everyone else in the ecosystem seems to be aliasing v12 to latest at the moment.

[dhensby]

I think it's worth putting this in.

Sure, but only once we can actually get it green :)