Check for 64-bit arch in setup.py

This PR adds a second check for 64-bit systems that fail to pass `sys.maxsize > 2**32`.
Python sometimes defaults to using i386 on x86_64 systems causing it to use 32-bit python and shoots out this error:
````
errors.NotSupportedError:
u"Your processor is determined to have a maxSize of2147483647,\n
which doesn't correspond with a 64-bit architecture.\n
Please contact CodeCombat support, and include this error in your message."
```
We can fix this by checking if the machine is x86_64 with `os.uname`. If it is we can safely assume the system is 64 bit and thus return 64.
I have only experienced this problem when trying to build on the macbook airs with brew installed python.