Fixes undefined function error thrown during model generation with schema

Fixes undefined function error thrown during model generation with schema:

$ sails generate model example name:string email:string
warn: For the record :: to serve the blueprint API for this model,
warn: you'll also need to have an empty controller.

/usr/local/lib/node_modules/sails/bin/utils.js:283
if (!isValidECMA51Variable(entity)) {
^
ReferenceError: isValidECMA51Variable is not defined