fix mapnik.Image.fromBytes doc
fix mapnik.Image.fromBytes doc

mapnik/node-mapnik,tomhughes/node-mapnik,tomhughes/node-mapnik,mapnik/node-mapnik,mapnik/node-mapnik,tomhughes/node-mapnik,mapnik/node-mapnik,tomhughes/node-mapnik,tomhughes/node-mapnik,mapnik/node-mapnik