Fix for ImportError on runnning build.py

Hey! I was getting this error...

$ python build.py 
[WARN] please update the LICENSE file with your license text before distributing
Traceback (most recent call last):
  File "build.py", line 216, in <module>
    build_module(manifest,config)
  File "build.py", line 161, in build_module
    from tools import ensure_dev_path
ImportError: No module named tools

and adding $HOME in the xcconfig fixed it. Hope that helps!