Pip package installation fails under directories with spaces

This is not specifically an OpenBazaar issue, but if you attempt to configure OpenBazaar under a directory structure with spaces on OSX (tested on 10.10 beta 5) it will fail with the error:

`./configure.sh: ./env/bin/pip: "[PATH OF FOLDER STRUCTURE UP TO SPACE]: bad interpreter: No such file or directory`

To bypass this, you can add `python` in front of the `pip install` commands to use the system python.

There may be a cleaner way of handling this, but in any case there should be a note about this issue somewhere so folks are aware.