Upgrade to latest mapnik-vector-tile version

[artemp]

While digging into compiler warnings I noticed we're still using mapnik-vector-tile 2.2.1 in https://github.com/mapnik/node-mapnik/blob/master/package.json#L39

Latest master has some important fixes and builds cleanly (no warnings) for me, shouldn't we upgrade? /cc @springmeyer @jseppi

[springmeyer]

👍 to upgrading.

[Algunenano]

You might want to update wagyu too. 0.5.0 should be faster in some cases and more robust.

[artemp]

@Algunenano - good call, I'll take a look, thanks.