Add npm as a dev dependency.

Former-commit-id: c72a6e13774bce378dd2ab5982f51ba37c6a7bc0

build/post-install.js

@@ -61,6 +61,7 @@
   npm.load({
     'global': true
   }, function(exception) {
+    console.log(path.resolve(basePath, '..'), npm.root);
     if (exception) {
       process.stderr.write('There was a problem loading the npm registry.');
       process.exit(1);