Minor fix regarding setup.py

Now, setup.py does not assume to be called from the path where the
source tree resides. This fixes getting the long_description and the
version if setup.py is called from outside.

instaloader.py

@@ -27,7 +27,7 @@ import requests.utils
 import urllib3
 
 
-__version__ = '3.0-rc0'
+__version__ = '3.0rc0'
 
 
 try: