package: update to "nan" v2 for native tests

Author: TooTallNate

package.json

@@ -26,7 +26,7 @@
   },
   "devDependencies": {
     "bindings": "~1.2.0",
-    "nan": "~1.7.0",
+    "nan": "2",
     "mocha": "*",
     "ref-array": "~0.0.3"
   }