Mvt update

Passes ``make check`` on a dev host with stdbase_devtools. More recent versions of mapnik-vector-tile need a mapnik upgrade.

https://github.com/mapbox/mapnik-vector-tile/compare/db13068ed981d312bdc8d72e3edb3661fa49571d...7fc006db2040efdfd06e9177eb7b906dc8f011e5