Update dependencies to get ready for node v6

src/main.js

@@ -6,7 +6,7 @@ var fs = require('fs'),
     path = require('path'),
     request = require('request');
 
-var mbtiles = require('mbtiles');
+var mbtiles = require('@mapbox/mbtiles');
 
 var packageJson = require('../package');
 

src/serve_data.js

@@ -6,9 +6,9 @@ var fs = require('fs'),
 
 var clone = require('clone'),
     express = require('express'),
-    mbtiles = require('mbtiles'),
+    mbtiles = require('@mapbox/mbtiles'),
     pbf = require('pbf'),
-    VectorTile = require('vector-tile').VectorTile;
+    VectorTile = require('@mapbox/vector-tile').VectorTile;
 
 var tileshrinkGl;
 try {

src/serve_rendered.js

@@ -16,7 +16,7 @@ var Canvas = require('canvas'),
     express = require('express'),
     mercator = new (require('@mapbox/sphericalmercator'))(),
     mbgl = require('@mapbox/mapbox-gl-native'),
-    mbtiles = require('mbtiles'),
+    mbtiles = require('@mapbox/mbtiles'),
     pngquant = require('node-pngquant-native'),
     proj4 = require('proj4'),
     request = require('request');