Revert "update Makefile & setup.py" (fix #685)

This reverts commit c3ac87a7a1c5f47aa4d4dc0c1d168a8f39840ea6.

Makefile

@@ -1,4 +1,4 @@
-SETUP = ./setup.py
+SETUP = python3 setup.py
 
 .PHONY: default i test clean all html rst build sdist bdist bdist_egg bdist_wheel install rst release
 

setup.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 PROJ_NAME = 'you-get'
 PACKAGE_NAME = 'you_get'