IPython paths set default for vagrant users

I changed line 471 so that it "defaults" to the user running this chapter "out of the box" through IPython where their path will be /home/vagrant/mtsw2e/ipynb

A user running these commands on their own env would know to comment that out :). Perhaps it might be nice to make this path dependent on a variable at the beginning of the notebook.
==
import commands
commands.getoutput("pwd")
=>'/home/vagrant/mtsw2e/ipynb'