upgrade nan

package.json

@@ -50,7 +50,7 @@
     "meow": "^2.0.0",
     "mkdirp": "^0.5.0",
     "mocha": "^2.0.1",
-    "nan": "^1.3.0",
+    "nan": "^1.5.1",
     "npmconf": "^2.1.1",
     "object-assign": "^2.0.0",
     "replace-ext": "0.0.1",