Fix: callback expected errors in first argument

lib/cartodb/backends/layer-stats/mapnik-layer-stats.js

@@ -177,7 +177,7 @@ function (layer, dbConnection, callback) {
     // to define the queries of the second phase
     queries.phase(() => firstPhaseQueries(queries, context));
     queries.phase(() => secondPhaseQueries(queries, context));
-    queries.run(callback);
+    queries.run(results => callback(null, results)).catch(error => callback(error));
 };
 
 module.exports = MapnikLayerStats;