Use correct MongoDB url for Module 4

See Module 4 video at: 0:22:05 node app.js failing at db connection
assertion point. This PR fixes for Start and End project urls - in the course Module 4's context database url should be local.

![20141226182523](https://cloud.githubusercontent.com/assets/14539/5558555/974cb68e-8d2c-11e4-9337-ce0941cfcecb.jpg)