use latest mapnik-vt to avoid compiler error with latest mapnik - refs https://github.com/mapbox/mapnik-vector-tile/commit/c8bfa8fed6045834205cc8731b213c8d83064aca
use latest mapnik-vt to avoid compiler error with latest mapnik - refs https://github.com/mapbox/mapnik-vector-tile/commit/c8bfa8fed6045834205cc8731b213c8d83064aca

tomhughes/node-mapnik,mapnik/node-mapnik,mapnik/node-mapnik,CartoDB/node-mapnik,langateam/node-mapnik,langateam/node-mapnik,tomhughes/node-mapnik,mapnik/node-mapnik,CartoDB/node-mapnik,CartoDB/node-mapnik,langateam/node-mapnik,langateam/node-mapnik,tomhughes/node-mapnik,tomhughes/node-mapnik,mapnik/node-mapnik,CartoDB/node-mapnik,langateam/node-mapnik,mapnik/node-mapnik,CartoDB/node-mapnik,tomhughes/node-mapnik