fix preprocessorcer stderr failures

[mapsam]

This is a PR to test the results of updated preprocessorcer fixes, which are just an updated version of mapnik core.

cc/ @artemp @GretaCB @springmeyer @BergWerkGIS

[mapsam]

Once these pass, we can discuss over at mapbox/preprocessorcerer#63

[mapsam]

Looks like we are failing on tilelive-vector again.

@jakepruitt any thoughts here? Looks like expected fixtures are different than our assertions.

[mapsam]

Good news is that preprocessorcer passes! @GretaCB @artemp @BergWerkGIS @springmeyer

[artemp]

Ok great, thanks @mapsam

[springmeyer]

@mapsam - this is failing still I think because you need to point at your custom node-mapnik build. https://github.com/mapbox/mapnik-swoop/blob/preproceswizard-stderr-fix/package.json#L14 is still pointing at master node-mapnik which will pull binaries built against this version of mapnik: https://github.com/mapnik/node-mapnik/blob/master/package.json#L8 which does not have @artemp fix to unreleased Mapnik core.

[mapsam]

I've let this fall by the wayside - will take a look at it tomorrow and hopefully get things moving again!

cc @GretaCB