Bump Python library to 4.0.0 due to backwards incompatible changes in fifo handling

Author: nilfm99

python/vmaf/__init__.py

@@ -4,7 +4,7 @@
 
 __copyright__ = "Copyright 2016-2020, Netflix, Inc."
 __license__ = "BSD+Patent"
-__version__ = "3.0.0"
+__version__ = "4.0.0"
 
 logging.basicConfig()
 logger = logging.getLogger(os.path.splitext(os.path.basename(__file__))[0])